For some time now my 91 SE has been running kind of rough at idle. It starts up right away in morning and idles pretty good. Once I shift into Drive with brake on the engine gets really rough and crazy. After about 3 mins this goes away and idles better. At all times the idle isnt completely smooth...there is an intermittent PUTT PUTT in the exhaust. If I turn the A/C on the idle smooths out perfect and PUTT PUTT from exhaust goes away. Driving around there is also a hesitation just off idle when leaving stoplights. Other than this the car runs perfect. Any ideas anyone? Why the perfect idle when A/C is turned on? Anybody experience somethin like this? Let me know...thanks

BTW, I replaced cap, rotor, plugs and wires recently..passed emissions check easy couple months ago.

 

Guess on rough idle smoothing with AC on is the rise in RPM's(albeit a small one) when AC is engaged. Maybe one of the resident experts knows better.

Other than that, I am VERY interested in the root problem/cause.

 

almost sounds like an injector on its way out.. minus the ac thing

 

Just wanted to add something, this morning when I first started the car, it was at its usual cold high idle(smooth). When I would give it gas slightly, the engine would shake/miss from 1000-2000 rpms. When I would let off it would smooth out again. Once it warmed up this went away.

 

I would say an injector is on its way out as well. I had a similar problem with my 93 SE and found that I had lost two injectors. The symptoms were much more extreme and it had 190,000 at the time, so that was to be expected.

 

Hopefully you have a tachometer analyzer that you can attach to the spark plug wires.... then perform a cylinder drop test at idle or the suspect rpm 1000-2000. Pull the spark plug wires and record your dropped rpm at the tach to determine the strenght of that particular cylinder. When you get to the bad cylinder/s the rpm drop will be less.
I would also perform a compression test on all the cylinders to determine if there is a sealing problem in a particular cylinder/s.
After you've located the weak cylinder/s and your compression test outcome was excellent, I'd definitely suspect the injectors....I would try cleaning them first either with a DIY cleaning additive and a nice long highway trip to burn off that tank of gas or having a shop professionally clean your fuel system which really works. Then if all that fails replace all 6 injectors with new....cause the VG isn't to get to when working on the injectors! GL hope cleaning them works!