86 GT with "surging" idle problem - Toyota Nation Forum : Toyota Car and Truck Forums

seann · 12-09-2009, 07:10 PM

Looking for some help with '86 5 speed, car runs OK, only 209,000 kms, compression good, ignition tuned, have replaced all vacuum lines, cleaned EGR valve (someone had jammed a screw in the lower port and plugged the vacuum line to the top with a ball bearing), as soon as the car warms up the idle floats very consistantly (about every 2-3 seconds) from 1000-1300 revs.
Tried several TPS settings, just moves rev range. Anyone had any experience with a fix for this?

Thanks

Rick89GTS · 12-12-2009, 02:20 AM

Are you low on coolant? Yes, I said coolant. If your coolant level is too low, the coolant sensor causes the car to cycle revs anywhere from about 800 to 1200 RPMS. Weird I know, but it happened to me.

The other things to look for are any air leaks or cracks/splits in the big air hoses that lead from the AFM to the intake manifold. Also check your AFM connections, but NEVER UNSCREW IT - it simply unplugs. Just check that the connector plug is making good contact.

seann · 12-12-2009, 02:08 PM

Thanks for suggestion...coolant within 1/2" of filler neck, topped it up, checked for coolant at hose leading to throttle body (in case it needed a burp). Problem still exists. Someone along the way has taped the intake hose, I peeled it all off to find several cracks so I cleaned it, retaped and checked for pressure leak with mityvac. The other thing someone has done was plug the lower pipe in the EGR with a screw, and plug the vacuum line to the top of same with a ball bearing. I vacuum/pressure tested the valve and it seems to be working, so I put it back to stock with the hose also replaced to the bottom of EGR. No change in condition. Back to head scratching. Thanks. Any other suggestions?

quote=Rick89GTS;3009736]Are you low on coolant? Yes, I said coolant. If your coolant level is too low, the coolant sensor causes the car to cycle revs anywhere from about 800 to 1200 RPMS. Weird I know, but it happened to me.

The other things to look for are any air leaks or cracks/splits in the big air hoses that lead from the AFM to the intake manifold. Also check your AFM connections, but NEVER UNSCREW IT - it simply unplugs. Just check that the connector plug is making good contact.[/quote]

Rick89GTS · 12-12-2009, 08:41 PM

The other things off the top of my head are the TPS and IIRC, there is something called the ISC valve (idle speed control) or something similar. I'm not at home right now, but I'll check it out when tomorrow.

If the air hose pressure checked OK, check your AFM. A fubared AFM will give erratic idle. Can you swap a known good one in and see if that helps?

seann · 12-13-2009, 10:39 AM

Any adjustment/specs for TPS and whatever else would be a great help, I've ordered a manual. Will put the word out tomorrow looking for a parts car. Can the coolant sensor be "tricked" to take that possibility out of the equation?

Quote:

Originally Posted by Rick89GTS

The other things off the top of my head are the TPS and IIRC, there is something called the ISC valve (idle speed control) or something similar. I'm not at home right now, but I'll check it out when tomorrow.

If the air hose pressure checked OK, check your AFM. A fubared AFM will give erratic idle. Can you swap a known good one in and see if that helps?

Rick89GTS · 12-13-2009, 08:48 PM

Dunno if the coolant sensor can be "tricked" but if you checked the level and it's ok, I'd rule that out. When it happened to me, I was waaay low b/c a freeze plug blew out and spilled out all my coolant.