Re: 87 Topaz - Idle varying between 1-2000
Has the minimum idle speed been checked? Minimum idle speed is the setting of the engine RPM without the vehicle's computer being involved. It's not uncommon, with age, for the minimum idle speed setting to change which can result in erratic idle speeds and/or stalling problems. There is a specified procedure for setting the minimum idle speed on your vehicle that must be followed. If the procedure is not followed correctly there are emission control systems that could become activated at idle speed, which is not supposed to happen. Also, the installation of poor quality aftermarket parts can create idle problems too.
The high idle problem may very well lay with a sticking throttle. You can remove the air inlet hose and take a look at the throttle plate and surrounding area. It is very likely all you’ll see is a bunch of black carbon. It is common for carbon deposits to build up on the throttle plate causing it to stick and cause the idle speed to be erratic. The fix for this is: With a soft bristled brush and rag in hand spray the area with some WD-40. Then scrub away at the throttle plate and the surrounding area until it is bright and clean. This is often the fix for a sticking throttle and erratic/high idle problem.
I would suggest having a qualified technician diagnose your running problem. Once you know what’s broken you can perform the repairs yourself. Most cases it is fairly easy to do and will cost you less if you can throw a wrench.