idle problem

my 91 tarurs with 3.8 idles strange sometimes mostly when the a/c is on when driving on hwy i can really feel what i believe is the compressor kicking on & off really bad and sometimes the trans. shifts funny and also it feels like its missing no check eng. light and seems to run and shift fine with a/c off. Please help i need to drive this car on atrip in 3 weeks.

Welcome to the forum!

Sounds like you may be due for a tune up. It sounds like you probably have a misfire that occurs under engine load. You probably want to start with a bottle of fuel injector cleaner added to the fuel tank, spark plugs, spark plug wires, check the distributor cap and rotor, and fuel filter. Also, don't forget to check the air filter, check the PCV valve, and clean the Mass Air Flow (MAF) sensor if your 3.8 has one. I don't remember if the 3.8 in '91 had MAF or MAP.

-Rod

done all of the things you said except maf sensor none helped

Okay, so how long has the car been acting this way? Did it just start after you filled up with gas? How recently was the tune up performed? Did you perform the tune up in an attempt to remedy this issue? Any other details that might help us help you?

-Rod

i got the car in july from my brother in law it had a broken motor mount and he was getting a new truck he said if i wanted it come get it.I replaced mount and when i drove it it was acting this way he said it had been doing it for awhile before the motor mount broke.tuned it up last weekend. Sometimes when it seems to be idling low and you put it in drive it will jerk really hard i believe that could have broke the mount.

With the car in park and the engine running, what is the idle speed? When you turn the A/C on, does the idle speed drop? How smoothly does the engine idle? Are you willing to purchase a can of MAF sensor cleaner and carefully clean the MAF? While you're doing that, make sure the air filter is not restricted. Also, make sure all the air inlet hoses are secure. Any little leak in a vacuum line or the air intake system could contribute to a misfire.

-Rod

i will check sat. thanks

Maybe Idle speed control not raising the idle enough when compressor engages causing the surge at idle??

rained here finally sat.& sun. didn't get to check anything. I not sure if the craftsman tack/dwell meter will work on this model .The car don't have a tack so not sure how to check r.p.m How can i check idle speed control?

Don't mean to jack the thread, just curious, what do they do to the car during "tune up"? change spark plugs? air filter? oil?

Many of the items are listed in post #2 above. If you are asking for a specific model year, you really should start a new thread (assuming you've already searched the forum and didn't find a specific answer).

-Rod