I have a 1991 RS 305TBI. The car starts and idles fine when in park, around 850rpms. However, when I put it into drive the RPM's drop like normal, and then the engine starts to stumble, RPM's drop to around 500 and the car ultimately stalls. I have a similar problem with the car in drive and turn the AC on.

I tried cleaning the IAC and have finally replaced it. I also had to replace the battery, not that that had anything to do with it.

Anybody have any suggestions????

 

when is the last time it had a tune up?

 

It only has about 8,000 miles since the last tune up. I tried a little more troubleshooting today. I started it up, and it idled around 1700 rpms. The rpms slowly dropped to around 1,000. I shifted it into drive, and it started to die and then stabilized. It did this several times and then held an idle in drive and showed 1,000 rpms. I messed with the AC, and the rpms would drop slightly as the compressor cycled, but the engine stayed running.

The only thing that I found to be weird was when I had it in drive and went to turn the steering wheel ever so slightly, the erratic idle happened. The rpm's had immediately dropped to around 500 and then it died.

The operating temperature at this point was around 200 degrees and the fan was running.

I repeated the motions several times and the only time it died was when I would turn the steering wheel.

?????

 

My Dad's 87 350 TBI did the same exact thing. I popped the dizzy cap and there was all kinds of yellow dust when I did a tune up. Problems started after the tune up. After throwing parts at it, it ended up being the distributor pickup. It had broken down and turned into yellow dust. My friends 87 T/A did the same exact thing. Pickup shot, yellow dust in the cap. Pull your cap and see is anything is up. Once we replaced dizzy's in both vehicles, they were fine.

 

Make sure your electronic timing control wire is plugged in. I forgot to plug mine back in after timing it and it did the same thing.