Rough idle and variable idle.

[corolliaxe]

Me:
Hey guys, firstly I just wanted to say I’m new to forums and I’ve looked extensively trough forums before deciding to post. Hopefully I can get a lot of useful advice from you experts. I’ll try and give back as much as I can, though my knowledge is quite limited.

Car: 1992 Toyota Corolla

Problem:
As stated above the main issue I have is a rough idle. Additionally, my idle seems to vary considerably from drive gear to park gear. When the car is in the drive gear and stationary my idle will be around 750 rpms. When I put the car in park gear my idle remains around 1100 rpms.

History of issue
Actually my idle was a lot worse when I first got the car. In fact it felt like the car was shaking itself to pieces every time I came to a stop light. The car would idle at 700 rpms, which I believe to be the factory preset idle speed. At this idle speed when any accessories came on, such as the radiator fan, the rpms would drop near the high 500's, and the engine would act as though it were on the verge of stalling. When engaging the park gear the car rpms would only jump to 800, still within the normal range, I think.

Attempted fixes:
After suspecting the throttle body (TB) for some time I took action and removed it from the vehicle. Cleaned it out with some carb cleaner I got at AutoZone. I also sprayed some into the Idle air control valve via the hole located before the butterfly Flap thingy of the TB. I didn’t however remove the IACV; I don’t even recall it being removable from the TB. I also removed and cleaned the screw that lets air bypass the TB, don’t know the name of this component; I just know it changes the idle speed. Anyways, I also cleaned that. I will also note that I did remove the electronic sensors before cleaning the TB, so I don’t think I damaged those in the process. To my surprise after putting it all back together I had a noticeable improvement in the engine idle, it was noticeably smoother but still rough.

New problem:
After doing this, now I had to finish the project by adjusting to the proper idle speed. After reattaching the TB and turning the car on, it idle around 650 rpms, an rpm the car doesn’t seem to like because the engine runs very shaky at such rpms. At this idle speed the rpms vary by less than 100 from drive gear and parking gears. I decided to adjust the rpms via the screw on the TB to around 750, which the car runs smoother in. The problem is that it stays at this rpm in drive gear but when I switch to the parking gear the car idles at around 1100 rpms.

Possible diagnosis:
I'm thinking maybe I didn’t properly clean the IACV. It’s possible that I didn’t clean it thoroughly enough. If so how would the problem manifest itself would be the question. I really don’t think this issue is complicated I just don’t know how to solve it. I'm a novice, so I will really appreciate any suggestions.