So I hears the deal. I own a Bmw 325i 1988( M20 engine) for awhile now ive been trying to figure a problem it has. simple enough I need help. As soon as I turn I turn the ignition, the car will start immediately. No hesitation, but once i do, the Rpm will pick up around 1500 rpm. once it settles around 900 rpm, i need to keep my foot on the gas pedal or it will shut off instantly. Parts iv'e already change;spark plugs, fuel filter, ignition cable, recent valve adjustment, Tps. MAF rubber boot. Oil change. O2 sensor. this car was my daily for 3 years. and would like to be driving it again. Any thoughts, Ideas, solutions?
Have you check the resistance on the crank sensor?
I am trying to think what could cause your trouble
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And, you have no vacuum leaks? It sounds like a vacuum leak.
No e30s again.
I believe the Crank Sensor (Pulse Sensor) in the front of the engine will cause a no start issue - open circuit - to weak reading - not an idle issue.
The idle could be from a vacuum leak as superj suggests.
Does the car run and drive (under load) with you feathering the gas - or does it die if you try and drive it?
Do you get a "Check Engine" light?
The car runs and drive for a little bit. Then it shuts off.
Have someone start it and put your hand on the exhaust. As it starts to die out, keep feeling the exhaust. Maybe your exhaust is clogged, or partially clogged, so it chokes the engine out as the exhaust warms
No e30s again.
Honestly - its tough to point you in the right direction with just the limited info. No idea if it will accelerate, no idea if the check engine light is on, no idea if you checked for vacuum leaks etc. etc. Still no idea if you can you keep it running with the throttle.. or does it die when you are giving it gas ? This type of info helps us understand what the symptoms are. The car runs and drives a little bit then dies - literally could be a couple of dozen things from fuel, spark, air, electrical. It also helps to know why did you replace the TPS? - was it bad? Rubber boot was torn - did this change the idle or did it stay the same - massive vacuum leaks can cause the car to idle strange - maybe you still have leaks - suggest other rubber may also be bad.
Guessing - If it always starts immediately - does not have to crank very long - even after dying - its probably not fuel related. I have a hard time believing its Crank Position Sensor - again cause it starts right away. But a CPS that is going bad can cause acceleration problems under load its not reading so you'll have a weak spark. If the Catalytic convertor is plugged - it usually causes back-pressure which causes misfiring and prolonged idling - it can cause reduced power under load and stalling - besides the stalling you don't mention misfiring, or poor power - so Im inclined not to think this is it either.
Your air intake and electrical (DME) is where I would probably start to investigate - If you have a Check Engine light - I think on your 88 model we can do a STOMP test. You changed the TPS can you do a STOMP test to see if the test works? A Stomp test will not work without a properly functioning TPS. - So if you cant get the Stomp test to function then this is a clue. Air intake signal is vital to idle - AFM may not be working properly, Idle control valve may be cause an issue, as earlier -vacuum leak(s) somewhere - On electrical - it could be a faulty DME - it also could be a faulty main relay - this actually just happened to me - the car would start but would stumble and even die at certain times - A true pain in the butt to isolate - I just popped in a new one since they are so cheap and haven't had an issue since.
If you get it figured out - let us know and or report back what you changed or tested. If you need a testing procedure for a component just ask we can help with that too.
I did see in your first post that it dies if you take your foot off the gas. I’m thinking two things. One, the new tps is not adjusted, or not working at all. It has to be set a certain way or it’s the same as being defective. Two, the idle air control is not allowing air past the throttle body. You could use the penny trick to see if it would idle with the icv in place, and/or try to clean and/or diagnose it to see if it’s getting power/ground etc
spark plugs, fuel pump have been changed recently. ^(95BMWIC) check engine light will come on and off. As for the exhaust^( superj) it had been changed out recently and have ruled it out. Yes the TPS was bad, so it was replaced. TPS Adjustments? Stomp test works, but what codes should I be looking for? ^(msservies) ICV has been cleaned out and in working condition.
If you keep the engine running by opening the throttle, does it have normal power? Or Does it still bog ?
What codes does the STOMP test provide? This might help point you in the right direction. You have to count the flashes - the codes are a series of 4 numbers - I believe there are 3 second pauses between each "number" So one flash - 3 sec , two flashes -3 sec, one flash - 3sec, one flash- 3 sec = 1211 or faulty DME. then it goes on to the next code - once you start seeing the same codes again then you have them all.
See code list here. http://www.unofficialbmw.com/repair_faqs/motronic.html
The TPS is adjusted so when the throttle butterfly is closed (idle) there is continuity (0 OHMS) to the DME. The DME should receive the signal at idle and at Wide Open Throttle. TPS must be working in order for STOMP test to work. I'm assuming TPS is working.
Why did you replace the fuel pump? Also - Can you keep the motor running with the throttle (For LIKE a FULL 5 minutes if you wanted - to get the engine warm)? Finally - do you have an extra main relay ( a used one or access to another E30)?
One more - you state the "exhaust" was changed - did you change the catalytic convertor also or just the pipes from the catalytic convertor (intermediate pipes and muffler)?
Last edited by 95BMWIC; 03-02-2019 at 08:38 PM.
I assumed there was issues with the fuel pump so I changed it with the spare fuel pump. As for catalytic converter it was changed with the down pipes. It was straight piped before.^msservirs. When the car turns over the rpms shoot up then goes down around 8-9 hundred. But I’ll have to hold on the gas for it to stay on, if not it shuts off.so yes it “bogs”.
Right, so it won’t idle on its own, but I’m asking if it has enough power to drive if you do keep it running with the gas peda
Because it could just be an idle issue
No e30s again.
Yes - like I said up in post #3 - this info is important - if it runs and drives with you controlling the idle then it suggest its not necessarily fuel related or spark (and thus CPS) - cause you have enough fuel and fuel pressure to run the car under load ..
and then this
You can narrow the focus on the idle... The RPM's you state in Post #1 can happen in cold weather (1500 then down to 900) - I would like to know if you run the car for awhile and let it warm up - will it idle then..
So more info..
What are the CODES?
Can you keep it running it for 5min?
Do you have extra main relay?
Once I start the car, it'll idle up to 1500 rpm's. With controlling the idle the car, the bimmer wont dye on me, even if the car warms up. As for the CPS, using a multi meter, the omens read lower than expected. one thing i'd like to know from guys/gals/ is when i accelerate theirs a delay. As in it takes a second for the rpm to go up after accelerating. I also wanted to do a smoke test. What's the best way on going about doing this???
CPS is not the issue as you can keep it running.
Going back to the top - your symptoms of hesitation rough idle sounds like a vacuum leak. Smoke machine is the best way to go -- but finding one is always a chore. If you can locate an old school mechanic they may have a machine - if not you can buy one from ebay...
I have never owned a smoke machine myself - you can put a vacuum gauge at the intake plenum to help diagnosis whether you have leaks or head issues.. Do a google search and you will see..
http://www.autospeed.com/cms/article...nostics&A=2393
Here in the midwest I pull 17 pretty constant. I would start with a vacuum guage if you cant find access to a smoke machine - to verify you have a leak.
So I’ve done a vacuum test and found a one major leak. The leak cam from the oil return pipe located under the throttle body. Once I got to replacing the o rings on ORP, I started the vehicle to resolve the next issues. I stared the car again having two issues. The bimmer starts and runs better after warming up. I press on the acceleration pedal and the rpm goes up but will have a delay before settleing down? And the aux fan doesn’t seem to turn on. Suggestions/comments.
aux fan would be a sensor. how long is the delay in idle drop?
No e30s again.
A few seconds till the idle drop. Idle settles down rough.where can I find the sensor?
One of the ones on the thermostat housing
No e30s again.
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