Low Idle

[Idrisu]

My E30 idles at 500/600 ever since I've bought it making take offs difficult and I know that’s not normal. I read that they normally idle at 800/900. I've tried all I can and need some help with this problem. Sometimes coming to a red light when I clutch and brake the car would almost stall and catch itself. So far I’ve replaced the pcv pipe, passed a smoke test no leaks, new fpr, rebuilt stock injectors, o2 sensor, air filter, and cleaned ICV. Any suggestions?

[E30xium]

Try messing with idle screw on the throttle near the throttle cable.

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[Idrisu]

Try messing with idle screw on the throttle near the throttle cable.

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looks good. has minimal slack like it should right?

[ak-]

Test your tps

[E30xium]

There's a small 2.5" Allen screw next that area that sits on the throttle switch. Try adjusting that screw.

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[Bimmerboy91]

I would also say tps. Also a dirty throttle body could affect your idle.

[Idrisu]

Replaced and adjusted a new tps. Didn't fix the low idle

[jlevie]

That sounds like a problem with the ICV or TPS. Normal idle with the engine at operating temperature is 750rpm.
The TPS and idle speed should only be adjusted once the engine management system is operating properly. With the engine at normal operating temperature, disconnect the ICV and use the idle stop screw for an engine speed of 950rpm. Then adjust the TPS so that the idle switch closes (as measured with a DMM) when the idle stop arm is 1mm off the idle stop screw. When you reconnect the ICV the idle speed should drop to 750rpm.

The best check for the idle (and WOT) switches in the TPS is done by removing the back shell from the DME connector and checking to see the proper inputs to the DME. That eliminates wiring as being a problem. After all, what is important is that the DME see those signals.

Oil can, and will, get into the TPS. The switches are simple exposed metal parts and oil will interfere with their operation. I always drill a 1/8”-3/16” hole in the center of the round boss on the bottom of the TPS to provide a path for the oil to escape.

Obviously, the idle switch is important for idle speed control as the DME won’t go into idle mode and operate the ICV if that signal isn’t reaching the DME. The WOT switch is equally important as it tells the DME to ignore O2 sensor data and to switch to wide open throttle maps, which will have a big affect on performance. Also note that above 4500rpm, when the AFM flap is all the way open the DME will be running in open loop mode using only engine temperature and rpm for fuel and spark advance if it sees the WOT switch signal.

As a side note, both the idle and WOT switches must function for the “stomp” test to work on a 173 or later DME.

IMPORTANT: Don’t mess with the idle air bypass screw in the AFM. It’s purpose is to set a specific CO level in the exhaust at idle. Adjusting the screw requires that the engine be operating properly and at normal operating temperature. The CO level of the exhaust is monitored and the bypass screw adjusted. This adjustment was made at the factory and should not be futzed with. If in doubt, get another AFM that still has the bypass screw sealed.