lumpy idle, stumbling engine

[kouks]

Still, if its rhythmic, its one cylinder. Maybe rent a compression tester from Autozone and do a compression test to see if you have a compression problem.

Losing any coolant or oil? Losing coolant along with this problem could be a HG problem, losing oil with this problem could be a piston ring/cylinder wall problem. Either one will show up on the compression test. If you're not losing fluids, and the compression test is good, then its fuel (injector), air (intake gasket or valve damage), or ignition (plugs, which you've already done). By any chance, have you done any recent work on the intake system from the air filter all the way to the throttle body just before this problem began? If so, could you have left a screw or broken plastic that could have been sucked into the intake and is jamming one of the valves? Assuming you've been driving like this for a while, that is an off chance since anything interfering with the valves would have cleared itself (plastic) or destroyed the engine (metal) by now.

Its too bad this car is OBD1 and you can't hook up INPA to see which cylinder is the bad actor. If you do have INPA, try hooking it up and running real time engine data and see if that works, you'll see it instantly. Then at least you'll know what needs attention.

[SwissCheeseHead]

Still, if its rhythmic, its one cylinder. Maybe rent a compression tester from Autozone and do a compression test to see if you have a compression problem.

Losing any coolant or oil? Losing coolant along with this problem could be a HG problem, losing oil with this problem could be a piston ring/cylinder wall problem. Either one will show up on the compression test. If you're not losing fluids, and the compression test is good, then its fuel (injector), air (intake gasket or valve damage), or ignition (plugs, which you've already done). By any chance, have you done any recent work on the intake system from the air filter all the way to the throttle body just before this problem began? If so, could you have left a screw or broken plastic that could have been sucked into the intake and is jamming one of the valves? Assuming you've been driving like this for a while, that is an off chance since anything interfering with the valves would have cleared itself (plastic) or destroyed the engine (metal) by now.

Its too bad this car is OBD1 and you can't hook up INPA to see which cylinder is the bad actor. If you do have INPA, try hooking it up and running real time engine data and see if that works, you'll see it instantly. Then at least you'll know what needs attention.

Thanks for the thoughts kouks. I ordered some RedLine SI fuel injector cleaner coming in today. I haven't driven the car much since the problem occurred. I didn't do any real work from the air filter -> throttle body, only after the symptoms were occurring did I check the air filter, clean/replace the MAF, so I don't think anything got pulled into the intake and lodged itself anywhere. I tightened oil pump bolts, re-did valve cover gaskets and plugs, changed out a coil pack that looked bad (had a chunk of something blown out). The car has always leaked a bit of oil, but never enough where normal oil changes wasn't enough. It leaked a bit of coolant, but never have I noticed that it was mixing in with the oil. The exhaust is "clean", no white or black smoke. PS pump squeaks when turning fully, but I'm thinking that's unrelated. The exhaust leak amplifies the pulsing (lumpiness) of the engine.

Crossing my fingers that the fuel injector cleaner clears out some possible deposits that might be clogging an injector or jamming up a valve. Am I totally off-base thinking that? It has gotten better after each of the "fixes" though. My next thought would be doing compression checks on each cylinder, and I would have to learn how to do that, which doesn't seem to bad if I can recall the general process.

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Does it feel like power surges on the highway at partial throttle?

Does not feel like a power surge. Power is steady all the way through the RPM range at WOT. When cruising with partial throttle, that's when the issue is really pronounced.

[ross1]

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Does not feel like a power surge. Power is steady all the way through the RPM range at WOT. When cruising with partial throttle, that's when the issue is really pronounced.

I think what Billyj was getting at is a vacuum leak.
WOT throttle running will usually be fine with this but part throttle(cruising), idle and off idle are effected most. If you are feeling a surging at steady state cruising you might want to look for vacuum leak(s).

[SwissCheeseHead]

I think what Billyj was getting at is a vacuum leak.
WOT throttle running will usually be fine with this but part throttle(cruising), idle and off idle are effected most. If you are feeling a surging at steady state cruising you might want to look for vacuum leak(s).

No surging at all really. Cruising at 50-55, when I have to apply the slightest gas to keep the speed at that rate, there is a stumble that is most pronounced when doing it. When idling, it's glug glug glug at a steady pace, and when accelerating, it speeds up with RPMs.

If it were a vacuum leak, would I jump into intake gaskets? Broken or loose hoses? What are the main culprits/easiest things to check first?

[kouks]

Cruising at 50-55, when I have to apply the slightest gas to keep the speed at that rate, there is a stumble that is most pronounced when doing it. When idling, it's glug glug glug at a steady pace, and when accelerating, it speeds up with RPMs.

The only vacuum leak that could cause this is an intake gasket failure on one cylinder. Everything at the throttle body and forward is not a culprit since this is rhythmic, only one cylinder is causing this, or one component.

First off, the steering pump could cause this if its wearing down and unbalanced. To check, remove the drive belt. Run the car for only a few minutes in the driveway. Do not drive it or you'll overheat it since the water pump is also not turning, neither is the fan. If the lumpiness goes away, it's a rotating component, and since you're saying the steering pump is making noise, it could be it.

A Torque converter that is going bad will act like you are saying. At any speed, not just 50-55, if you are cruising steady with no real throotle and then press the gas a bad torque converter can cause a chattering or stumbling feeling before the car gets going. You need to listen closely though. If you press the gas and the rpms respond, but the car is stumbling, it may be the torque converter. If you press the gas and the rpms and engine don't respond as expected, its engine related. When TCs go bad, they usually go bad fairly quickly, like within 50 miles of driving, mine worked for about 80 highway miles on the e38 from the first indication of a chatter until I got a TRANS warning.

A compression check is easy, usually less than an hour of work.

1. Get a compression check tool from Autozone (use their tool rental program, its free, you pay for it, then get a full refund when you return)
2. Remove all coil packs
3. Remove all plugs (I place a rag over the cylinders I'm not working on to avoid anything getting sucked into the hole. Do not stuff the rag in the hole, just lay over the general area)
4. Pull the fuel pump relay or pull all the fuel fuses to avoid any fuel in the cylinders
5. Attach the tool to each cylinder and turn engine about 5-8 times until max compression is reached. You can see the gauge pump up with each compression stroke. Use the same amount of rotations for each cylinder so you can compare equally if a cylinder is weak. You are using only battery power to do this check, so don't keep trying over and over again, make sure the tool is in place well, rotate the engine on the first cylinder until you get max compression, note the turns it took, do the rest the same.
6. If one cylinder is greater than 30 psi (I think) different than the others, you have an issue. What you're looking for is mostly consistent pressure between cylinders, one being way off is an issue.

Three things will cause bad compression.

1. A broken head gasket (this will appear as white smoke in the tailpipe, loss of coolant, or overheating...things you say you don't have) Spark plug may be green (on copper) or may have moist look.
2. Damaged cylinder rings or cylinder wall (loss of oil without an oil leak) Spark plug will be black with residue and maybe even have burnt oil on the igniter portion
3. Damaged valves. This can cause a whitish spark plug if the cylinder is running lean (too much air) or black plugs if running too rich (not enough air, too much fuel)

If compression checks good, then the problem is above the cylinders, which is a good thing, because you can fix a head gasket, the other stuff gets complicated. Valves can be redone at a cost, cylinder walls means get a new engine.

Sorry for the long write-up, will be interesting to find the problem. My bet is it's something simple, don't throw parts and $$ at it, eliminate the causes and find the culprit.

[SwissCheeseHead]

Don't apologize for the long write-up. This is precisely the reason why this community is so awesome! I'll further investigate and look into it in the next days/weeks and will update accordingly. I'll make sure to check each of the items on your list and report back. Thanks again!

[Sir Montalbon]

The only vacuum leak that could cause this is an intake gasket failure on one cylinder. Everything at the throttle body and forward is not a culprit since this is rhythmic, only one cylinder is causing this, or one component.

First off, the steering pump could cause this if its wearing down and unbalanced. To check, remove the drive belt. Run the car for only a few minutes in the driveway. Do not drive it or you'll overheat it since the water pump is also not turning, neither is the fan. If the lumpiness goes away, it's a rotating component, and since you're saying the steering pump is making noise, it could be it.

A Torque converter that is going bad will act like you are saying. At any speed, not just 50-55, if you are cruising steady with no real throotle and then press the gas a bad torque converter can cause a chattering or stumbling feeling before the car gets going. You need to listen closely though. If you press the gas and the rpms respond, but the car is stumbling, it may be the torque converter. If you press the gas and the rpms and engine don't respond as expected, its engine related. When TCs go bad, they usually go bad fairly quickly, like within 50 miles of driving, mine worked for about 80 highway miles on the e38 from the first indication of a chatter until I got a TRANS warning.

A compression check is easy, usually less than an hour of work.

1. Get a compression check tool from Autozone (use their tool rental program, its free, you pay for it, then get a full refund when you return)
2. Remove all coil packs
3. Remove all plugs (I place a rag over the cylinders I'm not working on to avoid anything getting sucked into the hole. Do not stuff the rag in the hole, just lay over the general area)
4. Pull the fuel pump relay or pull all the fuel fuses to avoid any fuel in the cylinders
5. Attach the tool to each cylinder and turn engine about 5-8 times until max compression is reached. You can see the gauge pump up with each compression stroke. Use the same amount of rotations for each cylinder so you can compare equally if a cylinder is weak. You are using only battery power to do this check, so don't keep trying over and over again, make sure the tool is in place well, rotate the engine on the first cylinder until you get max compression, note the turns it took, do the rest the same.
6. If one cylinder is greater than 30 psi (I think) different than the others, you have an issue. What you're looking for is mostly consistent pressure between cylinders, one being way off is an issue.

Three things will cause bad compression.

1. A broken head gasket (this will appear as white smoke in the tailpipe, loss of coolant, or overheating...things you say you don't have) Spark plug may be green (on copper) or may have moist look.
2. Damaged cylinder rings or cylinder wall (loss of oil without an oil leak) Spark plug will be black with residue and maybe even have burnt oil on the igniter portion
3. Damaged valves. This can cause a whitish spark plug if the cylinder is running lean (too much air) or black plugs if running too rich (not enough air, too much fuel)

If compression checks good, then the problem is above the cylinders, which is a good thing, because you can fix a head gasket, the other stuff gets complicated. Valves can be redone at a cost, cylinder walls means get a new engine.

Sorry for the long write-up, will be interesting to find the problem. My bet is it's something simple, don't throw parts and $$ at it, eliminate the causes and find the culprit.

Yeah, no apologies. That was a great read.

[kouks]

One trick on the intake gasket that is commonly used is WD-40.

As the engine is running, get a can of WD-40 and with the red tube attached, spray some liberally at the location of each cylinder's intake gasket area. If there is a leak at the gasket, the WD-40 will momentarily seal it and the rpms will change. It's a quick way of identifying a bad gasket without pulling the entire intake.

This method does not always produce consistent results so you may have to try it several times per cylinder to eliminate a leaky gasket as the problem.

[Billyj]

One trick on the intake gasket that is commonly used is WD-40.

As the engine is running, get a can of WD-40 and with the red tube attached, spray some liberally at the location of each cylinder's intake gasket area. If there is a leak at the gasket, the WD-40 will momentarily seal it and the rpms will change. It's a quick way of identifying a bad gasket without pulling the entire intake.

This method does not always produce consistent results so you may have to try it several times per cylinder to eliminate a leaky gasket as the problem.

Another one is to use chlorine free carb cleaner and spray near hoses and gaskets etc. If the rpms climb you sprayed fuel at a vacuum leak

[KVF]

Great information in here! I'm having a darn near identical issue with my e34 after an M62B44 (OBDI) swap/conversion. As I go through all of these checks/tests I'll report back if I find anything that hasn't already been mentioned.

[SwissCheeseHead]

In order to test using the WD-40 method or the card cleaner method, I'm assuming the only things I can take off are the engine cover and insulation pad right? Then I'm spraying around the edges of the intake manifold as described?

[KVF]

Yes. I like using brake cleaner because it evaporates quickly thereafter, but you'll still get a clear surge if you hit a leak. Whatever product you try, use the little flex straw to be as accurate as possible when you spray.


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[Billyj]

Essentially spray everything after the MAF to be thorough lol

I'm just joking... Kinda

[SwissCheeseHead]

Thanks guys! I'll stop and get some carb cleaner and try to get to this today.

[KVF]

Any progress on this? I tried the spray test and removing each coil while it was running and still can't isolate my issue. Wondering if you had any better luck.


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[ross1]

Yes. I like using brake cleaner because it evaporates quickly thereafter, but you'll still get a clear surge if you hit a leak. Whatever product you try, use the little flex straw to be as accurate as possible when you spray.


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DON'T use brake cleaner! http://www.brewracingframes.com/safe...sgene-gas.html

[SwissCheeseHead]

I haven't had a chance to try this yet. I just bought some GUMOUT carb/choke cleaner yesterday. Things have been busy and I'm not sure if I can get around to this tonight or tomorrow night. Might not be until Thursday.

[SwissCheeseHead]

DON'T use brake cleaner! http://www.brewracingframes.com/safe...sgene-gas.html

Thanks for the read. Very good to know!

[SwissCheeseHead]

So i found this using the carb cleaner method and got super excited

20170829_190438.jpg
It really helped smooth out the idle, and it runs less lumpy, but I'm afraid that it didn't resolve the issue. The problem still remains when I'm cruising at 50-55 mph with partial throttle, when it settles into gear and I have to apply just the slightest amount of gas to maintain speed. The engine stumbles and shakes. When I apply more gas and throttle to increase speed, it'll smooth out and cruising at 60+ will be much smoother, but the lumpiness is still noticeable.

Thoughts? I was thinking about removing and reassembling the throttle body forward to see if there were any other gaskets that might have popped out.

[KVF]

Glad you at least smoothed out the idle, but sorry to hear that the bog remains... It sounds like an issue that only occurs under a certain load, so I would probably be testing compression at this point. It's at easy as changing plugs and you can buy an inexpensive unit at any harbor freight or use the free rental at AZ.

My issue "may" be related to a failing ps pump that has a firm spot in its rotation, but I don't think that could account for a bog down at speed without at least some belt chatter. Good luck!


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[kouks]

So i found this using the carb cleaner method and got super excited

20170829_190438.jpg
It really helped smooth out the idle, and it runs less lumpy, but I'm afraid that it didn't resolve the issue. The problem still remains when I'm cruising at 50-55 mph with partial throttle, when it settles into gear and I have to apply just the slightest amount of gas to maintain speed. The engine stumbles and shakes. When I apply more gas and throttle to increase speed, it'll smooth out and cruising at 60+ will be much smoother, but the lumpiness is still noticeable.

Thoughts? I was thinking about removing and reassembling the throttle body forward to see if there were any other gaskets that might have popped out.

As far as the idle in the driveway, what you sprayed is the idle control valve (ICV). Replace the worn rubber grommet. You should also remove the ICV and you'll see a rotational valve inside. After years that valve will get gunked up and not rotate correctly, which affects airflow into the intake and idle smoothness. Spray brake cleaner in it while rotating the valve to free it up. Its good when you rotate the ICV and hear the valve freely clunking at the stops inside. Don't worry about the brake cleaner, that warning is when using it on hot metal.

On the high speed stumble, are you able to get this to repeat at a lower steady speed? By the time you are at 50-55 the car is in 4th gear. Can you get the car at a steady rpm in town at about 30-35 in 3rd gear and try the acceleration thing again, does it stumble at all then? Even a little bit? If it's repeatable at the lower speeds too, even if its less noticeable, it may very well be your torque converter. The only thing that troubles me is that TCs usually shred themselves in a short amount of time and this has been going on for a while.

Disassembling the throttle body from the intake manifold and cleaning is not a bad idea either. There are two hoses under the TB that get cracked also and may need replacement (on the M50 motor).

[SwissCheeseHead]

Hope you all had a good holiday!

KVF - thanks! and good luck to you in your search also.

I will certainly take apart the ICV and spray it with brake cleaner.

As far as the high speed stumble, I cannot get it to stumble at a lower speed (between 30-35) from what I can remember. It's not noticeable at all at lower speed. I thought it odd also that it only occurred when cruising at a certain speed/rpm range. I can try to do what you're asking an report back for sure, but for now, it's most noticeable at 55.

[SwissCheeseHead]

Car is sold so i won't be updating this thread anymore. Thanks for all the help guys!

[Tre0Tre34]

Sad Post

[kouks]

I wonder if the new owner will start posting about a lumpy driving engine soon...