So I have a 96 Corolla with 78k miles. Runs great but has a rough idle. On a cold start it high idles just as it should. Once the engine gets to operating temp and I shut off the car for a few minutes or an hour or so, the car starts and immediately goes into a very low idle, I'd guess about 200 rpm maybe less. The vehicle shakes vigorously but never stalls out, giving it a little gas during idle will stop it. After that the car drives and idle fine, rough idle, but fine.
I cleaned the throttle body with no noticeable change. I do not know the last time the car had a tune up done so my plans are distributor cap, rotor, plugs, wires, air filter, oil change, and while I'm in there, replace the Idle Air Control and Pcv.
Anyone have any thoughts?
Don't change any parts. That can get very expensive and frustrating with a trash can full of perfectly good parts that didn't need replacing and a lot less money in your wallet. There's absolutely no benefit to replacing parts if they don't need replacing, except for the discount auto parts stores who take your money. Further, just doing the parts replacement routine can introduce other problems into the picture, like poor quality parts that don't do their job well, or are defective, or are potentially installed incorrectly, etc. This opens a Pandora's box of problems that complicate diagnosing the original problem and can lead to a royal mess.
Instead,
diagnose.
If the spark plugs or spark plug wires were at fault, the check engine light would have come on, showing a misfire. If that hasn't happened, then replacing the spark plugs and spark plug wires, distributor cap, etc., will not cure the problem the car is having. It will however make your wallet lighter.
1. Is the check engine light turning on? If so, do you know what the codes are?
2. Have you had your cars onboard computer scanned to look for any stored trouble codes? Discount auto parts stores like Advance Auto Parts will do this for you for free.
3. Have you removed the spark plugs to look at them and see what kind of shape they are in?
4. Have you looked closely at the spark plug wires to see what kind of shape they are in?
5. Have you looked at the air filter? To see if an air filter is in need of replacement, hold it u to a strong light and if you can't really see the light through it very well, it's in need of replacement.
6. What procedure did you use to clean the throttle body?
7. Are you the original owner of the car?