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Need help m20 swap ( cant get to idle)

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I have a 75 2002 that i swapped a (1990) m20 with g260 trans. I Have been working on this car for the past 10 months got it running about 2 days ago. The problem i am having is it wont idle for the life of me. when u crank it up its starts out as High idle for about 8 seconds then it just immediately revs down then revs back up and just doesn't stop in that sequence. I tried swapping parts with my convertible that runs fine. I tried swapping air flow meter, Idle control valve. I looked for vacuum leaks with brake clean could not find anything. I also Put all new seals and gaskets except for the head gaskets have all new relay's (main,fuel,02) New crank sensor, timing belt exc. I am using the 173 ECU (dme). bosch 044 fuel pump. If their is anyone that could help me out or point me in the right the direction i would greatly appreciate. thanks.

-Andrew

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I will check again thanks for your info these things can be frustrating.

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Did you use brake cleaner or starter fluid to check for vacuum leaks. While brake cleaner is definitely flammable, I feel like it might also have a detrimental effect on the rubber intake boots and connectors. I'd try starting fluid next time, less chance of harming components.

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I have a 1989 325ix that exhibited those same symptoms. I also have a 1989 325iC. (Both are M20s, of course.) When I couldnt solve the fluctuating idle, I finally started swapping parts between the two.

My problem turned out to be the computer. When I swapped the two computers, the 325ix ran perfectly, and the 325iC now had the wildly fluctuating idle.

I swapped them back, and the problem returned to the ix, and the iC was fine.

I bought a replacement off ebay for about 65 bucks, installed it.... problem solved.

Do you have a way to swap in a known good unit as I did? I think one of mine was the 173 model, and the other was slightly different, btw..... but it didnt matter, as I recall. Day um, I just threw that old bad unit out in the trash last week too, after finding it in the garage. Otherwise I would get you the number off it. Sorry.

Good luck.

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Go search 'smoke test' at r3vlimited.

Jim Levie is the patron saint of intake leaks.

If it passes that test, then yeah, icv and ecu.

But smoke it first.

t

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You can always break out your bottle of propane and try to create a little rev as well.

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yes, for m20 issues, r3vlimited.com is a good source. idle fluxuation is an extremely common problem with m20's and there are a lot of well documented troubleshooting procedures.

did you pull the injectors and have them professionally cleaned?

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Thanks everyone for all the input. I have not

Had the injectors proffesionally cleaned I'm going

To try the smoke test tomorrow at work we have a

Smoke machine. If that come back good I'm gonna swap

Ecu with my convertible. One of the weird things that is

Happening is when I pull out the oil dipstick

It helps out the idle. And if I unplug the Icv

The car dies and the injectors keep spraying

Fuel when the motor is not running until I plug the icv back in.

Thanks again for all your help will keep you updated.

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This symptom is common in e30s. It's usually your idle control valve not working correctly. This can happen because it's not getting a signal from the ECU, which is likely if switching ICVs didn't affect your symptoms.

You should verify continuity from the ICV pins (there should be two) to the ECU plug. I don't remember the pin #s offhand, but you can get them in the ETM which I'm sure you have.

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if I unplug the Icv

The car dies and the injectors keep spraying

Fuel when the motor is not running

Ooo, it really shouldn't be able to do that- the ECU's SUPPOSED to

kill the fuel pump when rpm's drop below 300.

Be ready for the ecu (or something in its wiring) to be in error.

t

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