jw99ad

I've got an 87 Topaz that when in idle will sit at 1000 RPM - Race up to 2000 RPM - Then drop down to 1000 RPM. It will keep doing this until I put it in gear so I'm assuming it's an idle sensor of some sort (I could be wrong). Has anybody else heard of something like this and know how to take car of it. I was told by a garage that it could be an idle control solenoid or something similar. Any help would be appreciated.

LunaticSVT

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.

jw99ad

That helps a great deal. The quick fix ideas are something I can try in the meantime but I think I've decided to at least put it in and pay the coin to have the problem diagnosed. One mechanic I was talking to said the cars are notorious for faulty Throttle Position Sensors and that if that is the problem to not tackle it myself due to the calibration needed. When I started it today, it idled between 1200 and 1500 but that's still too high but not quite the large range as last time.

jw99ad

I got stubborn today and went out and started poking at hoses, changed the air filter, nothing seemed to be changing. Then I took a tester to the wires on the Idle Control Sensor and stalled the engine just by moving a wire. So I disconnected the ICS and cleaned the connectors. Got the engine started again and it was idling around 1000 and holding constant which was great. I'd been reading somewhere that if I scribed a mark on the side of the ICS and it's mounting surface to line them back up that I could take it off and give it a clean. So that's what I did, took an old toothbrush to it and scrubbed a pile of gunk off of it and from the little chamber behind. I gave it a good shot of WD40 and lo and behold when I turned it back over it was idling around 800-900 on the Tach and holding constant. The only test left to make sure it stays this way is to do a cold start in a few hours so it comes on at high idle because its cold and then knocks down to low idle. If it knocks down to 800-900 on it's own after a little shot of gas I'm in business. I'll let you guys know what happens.

LunaticSVT

How did this go? Did you get a chance to plug around with it over the weekend?