low idle condition

[fierofan84]

I have an early 84 with the 4cyl and automatic. The engine starts correctly, the high idle during warm up in choke mode is correct. As the engine warms up the idle comes down in steps like it should. With the car in park and fully warm the idle is about 900-1000. Drop it into gear, foot on the brake, the idle drops to about 500-600 and the car tries to shake itself apart. It does not like idling that low, put it back into neutral and the idle comes up and everything smooths out. Is there anyway to increase the RPMs with it in gear? I basically have to put it into neutral every time I come to a stop.

[Wreck It Ralph]

That’s not normal. Did you clean the ports for idle valve? May be built up with carbon not letting enough air it. May even need to pull the throttle body to clean the bottom of the ports.

[Raydar]

That’s not normal. Did you clean the ports for idle valve? May be built up with carbon not letting enough air it. May even need to pull the throttle body to clean the bottom of the ports.

This was exactly my thought. Carbon and crud in the idle passages can cause really odd, nonsensical symptoms. Pull out the IAC and clean everything in sight. Spray brake cleaner through the little passages. Maybe even take a pipe cleaner to it. (I've never done a 4 cylinder, but this absolutely fixed my V6 "bizarre idle" issues.)

[Fierofool]

I used a brass rifle bore brush and lightly twisted it inside my IAC port to clean it up a bit.  None of the cleaners I used would do the trick by themselves.  You have to be careful with anything you put in there so you don't scar the seat. 

[fierofan84]

I know what I'm doing before the Georgia game this weekend. That IAC seems like the first and easiest item to start with. Cleaning things carefully is usually a good idea.

[Roger]

Did the 4 cyl w/auto have a TCC?

[TopNotch]

Did the 4 cyl w/auto have a TCC?

Yes, same transmission as the 6, except possibly a different final ratio.

[Fierofool]

I would bring the car up to operating temperature then turn off the ignition, put a jumper into the ALDL then restart it.  Check timing.  It may be that timing is too low and needs to be advanced a few degrees.  The ECM will bring the idle back to the factory setpoint automatically after the ignition is turned off, the jumper is removed from the ALDL, and the engine restarted. 

Someone correct me if I'm wrong, but I believe timing has to be set with the vehicle in DRIVE for an automatic?

Just be sure the ignition is off whenever installing and removing the jumper.  Two lower passenger side terminals in the ALDL.