Hi Im Nate, have been looking and using community's knowledge on CL for a long time, but i have never posted. Now i have ran into a issue that my normal searching is not helping.......I have a 94 sc300 with pretty stock ge atm, I just did a 5spd swap with a r154, a stage 3 endurance southbend clutch, competition flywheel and the rear end is still at stock auto gearing. It drove fine the first day and clutch pedal was relatively light also. The next day i put on 3" straight through exhaust from the stock manifold.....Now when i start that car it will run fine idling about 500rpm after its nice and warm, if i push the clutch or have it in neutral. I take it for a drive and after a while if i come to a light and push in the clutch the rpms drop to below 300rpm and or try to stall, if i wait at the light either in neutral or with clutch pushed in it does not effect the rpm. If the car dies and is restarted, it runs at normal rpm for a while, until the cycle starts again......So does anyone know what would cause this?

 

Good day Nate
Try raising the idle RPM to 650 or 750.
Manual transmission car usually idle higher if i recall to prevent this type of issues from happening.

I got a SC400 and used to idle under 500 RPM in auto trim, i kept stalling once converted to manual till i raised the idle RPM.

Might also be caused by a dirty idle switch pump causing it to slowly respond

 

^^ This, and are you using the original automatic ECU or a 5-speed M/T ECU? That could have something to do with it. The weird idle issues could also be your AFM having issues or, as xtra also suggested, your Idle Air Control Valve might need cleaning.

This is a long shot but I had similar issues with idle and engine power after I had my R154 installed. They had NOTHING to do with the transmission swap (my car is also a 5-speed originally so my ECU was already M/T). The rubber intake tube had cracked right through which allowed unmetered air into the cylinders. This confused the ECU terribly. I was getting valve chatter from ignition timing being pulled as early as 4000 rpm. Once I fixed that-- issues solved.

 

thank you for the suggestions! I did check to make sure that all lines were connected and made sure there were no leaks past the MAF. So i went temp. adjusted my idle to about 1k rpm and it seems to make a big deference when driving and the issue has seem to disappeared ....I am running auto ecu, so does any one know how the auto ecu reacts when only having the neutral bypass done, yes it drives, but does it still react the same as if it were "drive" on the auto, ie in the timing advancement that normally occurs a little after 4k rpm.

 

HOw did you adjust idle? what do I adjust? pic please

 

sounds like an air leak. to adjust the idle look at the throttle body from the top (birds eye view). around the linkage you will see a nut and hex bolt with probably a dab of paint on it. loosen the lock nut, then use an allen key while holding the lock nut to adjust the idle. do it when fully warmed up only, and turn it clockwise to raise the idle.

 

Thank you..

 

Don't forget that you might have to readjust the TPS if you change the throttle stop nut.

 

excellent info you should reset the tps when making a change or it can think you are always on the pedal and not idling, then you get no decel fuel cut when you let off the gas and then you fail your next emissions test.

 

I never re-adjusted the TPS after i changed mine. But some advice when you do it, set your idle just below what you want, because when you tighten the locking nut it will increase the throttle. Also, you may want to make a reference mark on screw, nut and down.