Member
Hey guys,
So... i've gotten such a strange issue that really starts to eat me up.
The engine does not fall to idle rpm back down unless the vehicle is at a complete standstill.
If it is still rolling yet in neutral the revs keep bouncing every 2 seconds.
If i let the car rol in 1st gear, it revs up to about 1500 rpm and every couple seconds the engine sort of misfires bogs down and that cycle keeps on going.
Regardless if engine is cold or hot.
Cold start idle is also poor and surges a bit and runs a little bit rich... Mileage is still oke ish.
I've recently replaced the crank sensor, cam sensor, tps sensor, new fuel filter, coolant temp sensor, new spark plugs, full service etc.
Also thoroughly checked and cleaned the ICV, switched it out with an ICV from a friends car that has no problems so that is not the problem.
Also then replaced the throttle body gasket to be sure.
Also replaced a few vacuum hoses that were in doubtfull condition.
Smoke tested and can not find any vacuum issues.
O2 sensor replaced about 6 months ago.
However if i disconnect the MAF sensor the idle calms down right away.... so i thought well my maf is bad then...
So i swapped my maf with the one from my friends car and it still had the same problem, yet he did not.... so i conclude the maf should be good....
Driving me nuts...
Upped a small video on what it does when rolling in 1st gear, not touching any pedal.
https://www.youtube.com/watch?v=lp9I...ature=youtu.be
Last edited by Lucas325; 10-08-2018 at 05:59 PM.
Member
Well I would check more for vacuum leaks, maybe you need a better smoke tester. If the oxygen sensor has more than 50k on it then replace it.
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The O2 sensor has been replaced about 6 / 7 months ago.Originally Posted by Eric93se
I used a pretty accurate smoke test so... and i replaced anything with the slightest doubt.
It sounds way too regular to be a vacuum leak....
Member
I guess the last thing would be leaking injectors. Either send them out for service, or get yourself a good ultrasonic cleaner (don't buy the el-cheapo).
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I have this very same issue on my '93 325i M50B25TU (No O2 sensor | latin american market) I've tested so far:
* Vac. leaks
* Ign. Coils
*Spark Plugs
* Vanos
Pending check:
* Injectors (don't know why/how)
* MAF
* IAT/ECT
That problem is driving me nuts. It's been a while since I last drove my car with no problems.
Member
Hmm i can't imagine it to be the injectors honestly, maybe the fuel pressure regulator?
A "leaking" injector doesnt really happen so often. They are more likely to clog up and not spray evenly or at all when poor fuel is used and the fuel filter is never done.
Every injector tics good, always have ran on good quality petrol... not the crappy usa stuff, fuel filter done every 20.000km
The last 120.000 ish km was from my ownership.
I've read some strange things about the charcoal canister with the return fuel line that supposidly opens up every few seconds, anyone can elaborate on that?
- - - Updated - - -
Its friggin frustrating yes! I also already tried the IAT, did not make a difference.
Also changed the coolant temp sensor...
Member
The FPR? Does your engine crank too much before starting? It's my understanding that the FPR is bad if such symptom happens.
Member
That shouldn't be the case. There is a check valve in the fuel pump and what you can do is hook up a fuel pressure guage and check to see if the system is holding fuel pressure after the car is turned off.
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It's the MAF but I admit that it doesn't make sense that a known good replacement doesn't fix the problem. Mine did.
BMW used an oddball MAF on these cars, a 6-pin instead of the later model 4-pin, and when they go bad this is what they do. If you test it according to available documents it'll test good, but there's one wire that's not documented anywhere, the gray/white, that goes to the ECU and when disconnected from the MAF has 1.8volts at that pin coming from the ECU. If you remove this wire the engine will smooth out but it sets the check engine light. Reconnecting the wire restores the lumpy idle and also appears to drive the O2 sensor to maximum lean. The label is 'common' on the wiring diagrams which leads one to believe it may be a ground but it's not. I have a working and a non-working MAF but I haven't had the time to test that signal wire to see what's happening in a good and bad MAF. I'm guessing that the ECU is looking for some sort of PWM or frequency regulated connection to ground and this is what goes bad in the MAF electronics. I'll get to it eventually.
By the way, this particular MAF is out of production and the cost from the dealerships is about $1300 for one of these. Save your money on the $150 cheap replacements because they don't work.
Cheaper to buy a complete '93 to '95 2.5L replacement engine and swap the whole thing, with ECU. And, you'll get the variable cam in the process.
Last edited by tjm3; 10-10-2018 at 11:46 AM.
See ya later,
tony
'98 M3, '92 Dinan3, '05 R1100S BCR, '07 R1200S, Aprilia T
Member
Buddy, you know whats up!
I exactly thought the MAF, cause if i disconnect it it runs good idle and all... off course a bit rich.
But its suck fuckery that i changed it with an original bosch unit and it works in my buddy's car.
I know those cheap ebay things are crap and waste of money.
I actually opened a maf up, but its all smd, thought maybe there would be a bypass cap gone bad in it or so.
I'm gonna try to find another used original bosch.... Isnt there a way to rewire it to a later 4 pole maf?
Member
The later 4pin MAF operates differently than the one used earlier. The signal voltages are different and not compatible, especially with the original 6-pin MAF ECU.
I was lucky enough to find a good, used MAF and so everything is OK for now. But I've since decided to put a later model VANOS type engine in my '92 and bought
a used '94 2.5L complete with MAF, wiring harness and ECU to be installed when I get some time.
See ya later,
tony
'98 M3, '92 Dinan3, '05 R1100S BCR, '07 R1200S, Aprilia T
Member
So... The maf has been replaced and its 95% good now.
The only thing it still has is that after like an hour of highway driving...
If the car has to run stationary.... its shit.... It goes from proper stationairy rpm and dips down all the time almost dies and then the revs go up again.
Wont hold a steady rpm.
ICV has been checked, all hoses cleaned etc etc
Member
Ok this is a weird problem. Luckily I had a very similar weird problem about a year back and like yourself it was very frustrating to deal with because all the usual suspects were sorted.
The issue (for me) was finally traced to broken wiring between the ecu and the icv's connector. See even if your sensors are new, if the connector's wiring is busted you will have the same problem. Peel the boot back carefully and check if there are any breaks or stripped insulation especially at the head. If there are none, strongly suggest you do pinout/continuity testing from the dme clamp to the connector anyway- bad wiring can happen anywhere on the way to the dme clamp difficult to check sometimes (an easier repair might be to simply run new wires over the old ones). The B manual has the pinouts you will need. Also check on the coolant temp sensor and air temp sensor's connector.
Another way is to disconnect sensors one by one and test drive. The one with the bad wiring connection will lead to this problem stopping immediately - the dme will assume that sensor is dead and use default factory values which don't cause problems. However when you disconnect the icv remember that it will not hold idle and the engine will cut off if you let it drop to zero, so hold idle with the pedal at 700rpm.
Oh, you might want to pull the codes and see if that indicates any issue.
- - - Updated - - -
Actually just read this. It looks like the maf's wiring is the problem here.
Last edited by alang1990; 10-22-2018 at 08:06 AM.
Member
I'm seriously close at fucking demolishing this piece of shit car.
I had multiple bmw's for years, e28 e39 e46 e36.
And despite being besically good... if something is bad, it is a GODMOTHERFUCKING DAMN shit storm.
It's not the wiring, measured everything.
Car runs pretty damn rough on cold start, and when hot revs keep on dipping untill it almost dies.
When from stationary depressing the gas pedal it first almost dies and there is a delay before anything happens.
I am so seriously sick of this shit....
Member
You have a bad icv or bad icv wiring or both.
Test icv wiring when both hot and cold. If the pinouts are ok with no bleed through to adjacent wires in the same icv wiring bundle, then its the icv itself.
Its not enough that the icv buzzes when you switch the key to position 2. Its not enough to clean it and make sure there are no vacuum leaks in the two hoses connecting to it. If the car does not hold idle, if it hunts at idle, and there are no major vacuum leaks, and if unplugging the maf does not significantly alter this behaviour - its the icv's internal circuitry. And that you can't test.
Get a known good one. Used is fine they hardly get damaged internally.
Last edited by alang1990; 10-22-2018 at 09:21 PM.
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Below my solution:
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