Desperate, about to throw in the towel

[Vincent Brick]

I don't even know where to begin... I made another thread about my problems in the general tech section a few weeks back, but despite spending even more money and almost every minute of free time on it my problems persist and I am running out of cash.

I'm not sure how to describe it, but part throttle cruising and light acceleration its like the motor pulsates, it feels like you are constantly on and off the gas slightly. When engine braking, the motor will randomly sorta rev and buck. When accelerating from a stop, its like you have to wait for a one count before it builds enough revs to move. Give the motor too much gas too quickly and it almost wants to die. When accelerating through the RPMs it gets choppy above 4k or so. When the motor is cold it bucks a lot and will randomly want to stall. The throttle response is so bad it makes it hard to shift smoothly. The idle is sometimes erratic and always very rough. It gives no codes on a Modis scanner or from a pedal stomp test. My roommate works at a BMW specialty/racing shop and he says it is way slower than an M20 car should be. I've been learning about the Bosch AFM and trying to play with it, and it helped some I think, but rich or lean it doesn't help the pulsating sensation. I might be able to put it on the chassis dyno/wideband at my work (I work for a turbo accessories manufacturer, we don't have a mechanic on staff), but I'll probably have to pay a few bucks and I'm not sure it is worth it. And it randomly gave me a CEL at a stop light today, but then went away as soon as I pulled away.

I have replaced: plugs (NGK copper), wires (Ireland), cap & rotor (Bremi), injectors (refurb M50 greentop), fuel filter (Mahle), O2, crank sensor, cleaned injector and main engine harness connectors, adjusted valves, fixed all vacuum leaks (tests good on smoker), bent AFM wiper arm to contact fresh track, and I am sure I am forgetting other stuff. Of course that doesn't count all the money I have had to spend on stuff not related to the motor, and I need to put a rear end in it and a LOt of other stuff too.

I commute 65+ miles every day and if I can't get it running right soon I am going to have to get something else and sell my E30 for a huge loss. I'm in good with the owners and employees of 2 different BMW specialty/racing shops, but not good enough for free labor and I can't afford to pay them to look at it. I just don't know what to do, any help you guys can provide is greatly appreciated.

[DesertBMW]

When I buy old E30, what I do is, I pull the engine and just tear it down and just fix everything that is worn, I always find some hidden things that I never would have found diagnosing it.

[mpowerful]

Checked the iacv and tps?

[dnguyen1963]

The only thing that you have not mentioned is checking all your grounds. If one of them is loose or dirty you can experience this kind of problems.

[Dirty325ix]

That sounds like vacume leaks and I bet your check engine light turns on after 10 seconds at a constant rpm......have it run in your garage till the cel light comes on and then turn it off immediately.. then the code will show up with stomp test And I'd put money its your air fuel mix.

[raudonis]

Holly changing random parts Batman!

Have you tried disconnecting AFM or o2 sensor altogether?

Start engine, disconnect AFM and see how the engine work is affected, reconnect - note if there are any changes.

Same procedure for O2 sensor.

[e21jps]

intank lift pump or more likely high pressure fuel pump would be the first things would test.

pull the return fuel line off and get another piece of fuel hose, connect it to the regulator and run it into a bucket or gas tin and start the engine

you should get good clean flow of fuel squirting into the bucket, You can time it and work out flow rate, i cant remember the flow volume but should be something like 15-20 Liters/min?? someone correct me if im wrong

edit: ok divide above ammount by 10.... thanks raudonis

if the fuel is full of bubbles and spluttering and stopping or anything like that then replace the pump

[raudonis]

Amounts of fuel to be pumped thru the FPR in 30 seconds with engine off (fuel pump relay jumped, pins 30 and 87 or 87b):
700cm3 for m20b20
750cm3 for m20b23
850cm3 for every other m20
Any less than that - your fuel pump is done.

BTW, this is taken from this German book:

[jlevie]

My guess is that there are intake leaks (have a smoke test run) and that the WOT switch in the TPS is bad.

[crappycoco]

Does the problem persist when the car idles? I think that its either the fuel pump or something in that system or the computer. I would check both.

Do you have any means of changing the motronic unit for one that works 100%?
I would check that. Just change it and try to drive it. Could even be the green box above it but afaik thats responsible for idle.

[e21jps]

Try unplugging the TPS go for a drive it should be different in some way if its not then check the wires and maybe try another TPS

[Vincent Brick]

Lets see, where to start....

TPS tested good with multimeter.

IAC I suppose I need to retest, but that was one of the first things we checked when I started trying to fix it. I forget the test procedure but I know we checked it. My boss thinks it is IAC related, but he's an engineer for turbo systems not a mechanic nor experienced with BMWs, so I don't know how valid his opinion is.

If I disconnect the AFM I get a CEL, not sure if the car actually runs any worse. The time I accidentally started the car without the AFM and IAC plugged in, and the time I mentioned above where it come on briefly at a traffic light, are the only times I have seen the CEL come on.

I haven't tried disconnecting the O2. When I first got the car the Modis said the O2 was bad, I put a new one in it and it was supposedly good. That was back in paril or May though, very first thing i replaced along with the crank sensor. So I should disconnect the O2 and see if it runs any different? If it seems to run the same, what would that indicate? Wiring problem?

I don't have access to a known good DME. Would it be worth it to buy one? I'll have to acquire some container for measuring fuel coming out of the return line, and I'll research where all the grounds are and check them.

No indication of vacuum leaks last time I put it on a smoker, though I am starting to think that is the problem anyway. There are visible cracks in my intake boot, but my roommate (the BMW mechanic) says that is normal and as long as no smoke comes out it should be good. Trying to spread the cracks out with the car idling does not make the idle change. In inspecting the brake booster check valve, I managed to break a piece off (surely that will cost me another fucking $50) and create a very obvious vacuum leak, and plugging/unplugging that leak produces no change in idle beyond the typical variations. Should I buy an intake boot anyway? I have access to a different smoker, should I try it?

Almost everything I have done to the car has noticeably improved the way it ran, it was much worse when I got it, but I didn't realize how bad on the test drive because the previous owner wouldn't let me take it out of his neighborhood due to being uninsured and I never got it above 20mph.

I don't have the space or time to pull an engine out or tear much down, I can't own a project car right now but kinda got stuck with one I have to daily anyway. I act like I want to throw in the towel, but the reality is that I am in too deep and am unable to financially, I have to make this work somehow, I just keep getting frustrating because it is absolutely consuming my life and there is no end in sight. Thanks A LOT everyone for all the suggestions.

[Vincent Brick]

Main engine ground looks good, what other grounds should I be looking at?

The valve cover gasket was replaced recently, but I adjusted the valves after that, using the same valve cover gasket with a thin layer of RTV around. This was after the last time it was on the smoker. Could that cause a significant enough vacuum leak to do this?

[e21jps]

Fuel pump!!

[Ether-D]

My guess is that there are intake leaks (have a smoke test run) and that the WOT switch in the TPS is bad.

This could be why you get nothing from the stomp test.