Hot start/hot rough idle mystery

[clockwork]

Hi all.
So before I get the "Search" answers, I have to say I've done lots of searches over the last few months and still nothing has solved my problem even though I've been throwing new (but thank god not expensive) parts into her.

SO my problem is when I start the car with a cold engine it runs PERFECTLY and even drives perfectly till engine heats up.
After it heats up, if I'm at a stop light/sign, the idle is very erratic and drops so low all lights fade in quickly on the dashboard, as if the car has stalled, but then the engine revs up high and so the dashboard lights disappear again and the car does this little "dance" for a few seconds just as I come to a stop. If I sit for about 30 seconds, it seems to regulate itself to a nice idle.
Also if I was to turn off the car and restart it again after 20 mins, it cranks a lot but sometimes does not catch or it will catch and start but have the same erratic idle as when I have the car stopped with a hot engine.
Also noticed that when the engine is hot, the gas pedal response seems to have a lag (especiallly if I hit the gas pedal hard) from a stopped position and at times has almost caused the car to loose RPM's all together and die till the car saves itself (by reving rpm's high) and then the car drives away. kind of a scary feeling when at a stop light cause cars behind me start moving towards me.

So I've researched the popular "rough idle" threads and have replaced my FPR's, ignition coils (with MSD 8207 coils), PCV's, installed fuel line check valves at firewall and even checked the DK's out.
I did replace my fuel filters about 30k kms (18k miles) ago and most, if not all of my fuel lines have been replaced over last 2 years. Valve Cover and Intake Manifold Gaskets were done about 15k kms ago (10k miles) and I have even tested for vacuum leaks.

Anyhow, any other suggestions as what to check??

SOLVED - Time will confirm. I believe I solved this rough idle mystery after driving car and coming to a stop and having car almost die. I replaced the batt on the right side in trunk. Its the starting batt. I replaced and so far alllll those problems have gone away. the batt I took out just would NOT hold a charge period yet the alternator system was strong enough to keep it charged while driving at speed, but when idling, the batt couldnt keep up with load requested by car. Hence why car would almost stall, and now 2 weeks ago it woudln't start car even if driven for 30 mins at 100 km/h and then turned off for 1 minute and re-started. The replacement batt has NO issues.


Cheers, Mike

[53helofe]

Sounds like it could have something to do with a temperature sensor, or possibly a CI sensor works until it gets warm? I'm not going to lie, that could be a pain to track down but should be a simple fix after you do. At least it sounds like a consistent problem which gives some guidance.

[clockwork]

yeah I read your thread about the MSD ignition and I got hopeful it would solve it for me. no such luck, but at least I have nice shiny new red coils in the engine bay now

I believe it to be a sensor too.
What does the CI stand for?

[cartoonz]

pull all the stored codes for a start.

[53helofe]

I believe it to be a sensor too.
What does the CI stand for?

It stands for Cylinder Identification if I remember correctly. They are the little round doughnuts, one on each set of plug wires. The only way to change them is to buy an entire new set of plug wires or to change just the sensors you have to cut the original boot off and buy the new boot and connector for the wire but beware it is not like a standard set of connectors for plug wires like on other cars.

I thought I saw a post not too long ago someone posted about replacing them and showing what to do....

If you go to wuffer.net you can find the repair manual that gives specs on the sensors so that you can measure them cold then when it is hot and not running well measure them again to see if that is the problem.

[clockwork]

I thought that is what you meant.
I did just test and replace the spark plug leads to be honest with you. my 6th lead was not working so I replaced it with another 6th lead from a friends set.
Maybe I'll just try a whole set this time to rule the two CID sensors are not the issue.

[TxGR8White]

Might want to check the water temp sensors in the rear crossover pipe. The one for the DME's (has three pins instead of two), can easily have one side fail. When this happens, the engine management gets confused. If one side reads correctly, then that side of the engine has correct fuel delivery, etc. If the other side is faulty, then it will read much colder than it actually is and add fuel (makes the mixture richer) to that side of the engine, resulting in a stalling/rough idling condition. If you haven't replaced those temp sensors (actually all three), it would be prudent as it is part of preventative maintenance.

[cartoonz]

far easier to just plug the thing into the diagnostic computer and have the car tell you what's what.

Sure, all the suggestions here are real and can/do happen, but you're way better off actually using the technology built into the car to narrow it down first.

[clockwork]

I just need time to bring it to my mech to scan it really. Figured I could knock a suggestion or two off as well.

I will look into the 3 temp sensors at rear of engine. Thanks.

replaced them.

[cdnalpina]

Bring the car on Sunday - I can scan it for you

[clockwork]

Thanks to Rob, we found I had a few codes ((DME coolant temp sensor failure (highest of the three sensors at back of engine) and one for the MAF cyl 1-6)
So I replaced the sensor and got rid of that error and then I replaced the MAF with another used one and car seems to run great now (when engine is cold).
Will have to check after longer drive but all codes were erased and never came back since and car sounds a bit better and more responsive to the gas pedal.

[clockwork]

well I wonder if this Hot Start (which is rearing its ugly head again) is connected to the code 201 I'm getting through DIS5.7...
I've been getting that code for months now with no adverse reaction to the car's operation, but last night I drove the car for 35 mins then after about 15 mins of rest I tried to restart and the starter is perfect but the car is not catching and when it does I have to press gas pedal to help keep it going, and even then its sketchy. WHen it does catch it revs upa nd down highly while the lights on cluster illuminate then fade out, then in again till I can feather the gas to keep it running.

Oh the joys.

I'm thinking two KNOWN good working MAF's and 2 fully rebuilt DK's will rule out issues. I'll check the NEW FPR's again. I wonder if it could be the fuel pump either. I know a friend had that issue with his car with same hot start issue... it IS the original and at 225k kms. just ideas till I can get computer (DIS 5.7) back on to check for errors.
Luckily no steady C.E.L. is on.

[clockwork]

believe I solved my mystery by installing another battery in place of the right side battery (which I just learned died period). this replacement batt seems to have solved the problems I Was getting at idle speeds. See revised OP

[8eights]

Just to be sure, Wiggle the battery cables on that same battery while the car is running and take notice of any idle changes.

[clockwork]

Code 201 issue seems to be solved (can confirm in a day). DME itself is causing the problem. I cant believe it could be that, but since I've changed EVERYTHING else then wow, glad I finally caught it (fingers crossed)

[shogun]

So you changed one of the DME's and now the problem is gone?

[liquidblueloft]

Code 201 issue seems to be solved (can confirm in a day). DME itself is causing the problem. I cant believe it could be that, but since I've changed EVERYTHING else then wow, glad I finally caught it (fingers crossed)

finally... that was a process hey?

[clockwork]

Will confirm tonight. Package was not delivered yesterday. So "Christmas" has been put off till tonight, I hope. Will confirm.

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[clockwork]

Wow. Ok so changing the DME out and putting Wokke chip in new DME did not change things. Still code 201 in DME 1 slot. So I swapped DME slots and still DME slot 1 showing code 201. Its sooooo frustrating cause sometimes the code swaps DMEs/cylinders/banks. But not now.
F!!!

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[dragon850]

Wow. Ok so changing the DME out and putting Wokke chip in new DME did not change things. Still code 201 in DME 1 slot. So I swapped DME slots and still DME slot 1 showing code 201. Its sooooo frustrating cause sometimes the code swaps DMEs/cylinders/banks. But not now.
F!!!

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OK, all that code means is the mixture is out of adjustment parameters, hook up INPA and you will be able to monitor the fuel trim. How are your FPRs doing?
Usually this code goes away after the first 100 mile driving cycle is complete.

[liquidblueloft]

Mike...i'm starting to think that maybe our cars just don't like living in Alberta. lol

[clockwork]

OK, all that code means is the mixture is out of adjustment parameters, hook up INPA and you will be able to monitor the fuel trim. How are your FPRs doing?
Usually this code goes away after the first 100 mile driving cycle is complete.

new fprs and tested functionality.
i will play with INPA tomorrow.
the error comes back till I clear then back right away.
just curious why it switched banks a few times

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[BMSman]

If you hook up Inpa would you mind doing me a favor and check to see if you can talk to the EML when the engine is running? On my car I can only connect to the EML when ignition is on but engine not running. The DME's respond just fine when the engine is running but for some reason not the EML. I'd like to know if this is normal or not. My car is 91 850i.

Thanks!

[clockwork]

If you hook up Inpa would you mind doing me a favor and check to see if you can talk to the EML when the engine is running? On my car I can only connect to the EML when ignition is on but engine not running. The DME's respond just fine when the engine is running but for some reason not the EML. I'd like to know if this is normal or not. My car is 91 850i.

Thanks!

Just checked using DIS5.7
Ignition on, engine off: EML is readable.
Ignition on, engine running: EML cannot be found.

[clockwork]

Mike...i'm starting to think that maybe our cars just don't like living in Alberta. lol

Agreed or more sensitive to ignition.
I just swapped my OE MAFs I just got from Olin and the error followed. So I'm going to swap back in one of my other OE MAFs I've determined is not bad and see what happens...
Wish me luck. That means out of 5 OE MAFs, at least 2 are making the car not happy. I will pay to get them rebuilt after I hear some others compliment the repair company Taylor Patterson has recommended in another post.
They are NOT cheap to repair an OE MAF!!!!


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