I just put in my new motor into my FD. I drove it about 80 miles with no problems. Put all of a sudden it began to idle at high rpm's between 2,000 and 2,500 and it continues to rev and polsate at those rpm's. Sometimes it will go back to idle speed of around 800 rpm's but rarely. It does this weather I am driving it or at a stop light.
I would appreciate any help I can get to help me solve this problem. Where do I start looking? What could be causing this?
Thanks for all of you experts out there future help!

Sincerely,
Red FD3S that's not running good...

 

new or rebuilt motor?

 

I find it hard to believe that would have anything to do with his symptoms. Search for Chuck Westbrook on this forum, I forget his user name but it is something cew7xx. Order his tuning notes and it also comes with instructions on how to properly set your idle on your fd.

 

Are you on the stock ECU or a programmable ECU (PFC or something similar)?

 

yea if your running the PFC, you need to have it learn the idle. idle for 13 minutes, then idle for 13 min with AC on, then idle for 13 min with Defrost on.

Could also be a vac leak.

-mark

 

Check everything along your intake. A big vacuum leak might cause the idle problems. A bolt might have come loose or a gasket could have dislodged.

 

I'm sorry, i was not trying to diagnos his problem, i was actually more curious if he did pick up a brand new motor, or had it rebuilt by someone. Maybe, i should've been more specific.

 

if its stock ECu look for a Vac leak somewhere.

Does it boost fine?

 

Had similiar problem some years ago and it was bad lower intake gasket.

 

ya start looking for vacuum leak.

 

chagar, how bad a job was it to replace the lim gasket? I have the same symptoms, and in the bazillion hours of troubleshooting that I have done, it seems to be the most logical idea. I am just procrastinating because I fear that this is going to be a crazy hard job.

 

IF your car is sequential it will be a decently tough job, especially if you dont have a lot of experience doing mechanic work in a fd engine bay, if it is non-sequential it will be slightly less of a pain.

 

After a lot of investigation work on the website archives I was able to go strait to the BAC system and check both my AWS and IAC. I checked the AWS and it was clean and had no leaks. Also I had no problem with the AWS in the fact that the car on warmup would hit 3,000rpm and after 17 secounds go down in idle. When I checked the IAC it was stuck open at least a quarter of an inch from the seat! I soaked it in solvent for an hour and that released the shaft. I then oiled the hell out of it and moved the valve back and forth to make sure it operated freely. I check the coil and there was 12.5 ohms of resistance. I reinstalled the IAC and now everthing works just fine. The idle stays at 850 amd never strays! Thank God that problem is fixed