OK, I have been dealing with a nightmare here. I just put in an engine that idled and ran fine, but had the 3800 stumble. The other night I took the car up to 6000+ RPMs to make sure that it would still run well after 4000 RPMs and afterwards the car idled at around 500 and will stumble. Before it idled fine. Now it idles like crap ever since I ran up the revs.
Any ideas?

 

Maybe idle screw vibrated loose? check everything out in the TB and make sure nothing is wrong. If you give it gas will it still run fine?

 

that happened to me once and it turned out to be a hose that went into the intake manifold had fallen off. try checking to make sure of the hoses are
in. the hose that was off on my car was on the passerger side.

 

I just checked my hoses and all look fine. And yes, the car runs fine with a tap of the gas, just doesn't want to idle steadily anymore...

 

See if the bac plug fell off or is loose. If it's on good, then idle the car fully warmed up and remove the bac plug. Did the car die or the rpm's change any??? Or if you have a airconditioner.......idle the car and turn the a/c on. The rpm's should pickup with it on. Did any of the above happen? No a/c? Then turn the headlights on along with the heater fan and the rear defroster. Did the idle drop, car die etc when you did that? Probably but answer anyway.

 

this isnt a hijack my car idles rough too.. i thought it was the TPS so i adjusted it, and it still does.. when i turn my AC on it doesnt drop.. but when i turn my electric fan on it does a little. i havent checked my bac valve yet but i just thought id add this in, and see if anyone has any comments about that since its almost the same thing. thanks

 

Back in August I really hammered (For the first time-4000 miles) the engine installed by KD in 2002 through first and second. Developed an eractic idle afterwards and continued to idle rough. Disconnecting BAC, RPM's dropped, a/c on idle raised. Turned out to be the seal inside the BAC was leaking air. Tried cleaning, worked for about a month and started again. Replaced the BAC now now problems.
Still can't understand why the BAC would act up after a hard run, but that's what happened to mine. It's been fine since the replacement, no problems.