bucking/surging at idle

psychII · 07-02-2008, 09:34 AM

Well, my 86.5 A/T had developed a nice habit, just started Monday. Here are the symptoms (not sure if related):

1) when I crank the car hot or cold, the engine revs as usual, but then the tach needle bottoms out, almost stalls, revs, and settles in at usual idle RPM.

2) sitting in gear idling, she will buck and surge, but will stop once I accelerate/apply gas. No problems until I stop again.

This just started after a fun run through the mountains the other day. Spark plugs are new, wires are newish and look okay, fuel filter is new. Any ideas where I should look? MAF?

Thanks in advance!

porken · 07-02-2008, 10:44 AM

Since it happened all of a sudden, check for obvious vacuum leaks, and if the idle switch is connected/working. It could also be problems with the MAF or O2 sensor.

Check for ground at pin #3 on the LH connector for the idle switch, or connect a timing light and see if the idle advance is ~10°. If it is ~20°, then the idle switch is not working/connected. Too high advance at idle will make it buck.

(LH 2.2 connector pinout)

FYI: I'm going to have a kit soon to make it easier to set the base idle, and base MAF setting for LH2.2 32Vs.

info

psychII · 07-03-2008, 03:29 AM

Thanks, Ken. I will look at the possibilities you mentioned. I spent yesterday changing spark plugs in my Expedition, which is about like a motor-mount change in the 928 (not realy, but a big PITA).

FYI, I would love to have my 86.5 putting out the power yours is. You need to write a manual outlining how to do so (sell?). A lot of what you are doing is over my head.

psychII · 04:54 AM

nm

psychII · 07-05-2008, 03:50 PM

Well, after some fiddling, I found the culprit... an unplugged diagnostic connector.

I had unplugged it some time ago when replacing the orings on the water manifold and must not have secured it back. It evidently worked itself off during my drive.

Whew, sharkie lives to fight another day.

Shane E · 07-05-2008, 08:14 PM

Quote:

Originally Posted by psychII

FYI, I would love to have my 86.5 putting out the power yours is. You need to write a manual outlining how to do so (sell?). A lot of what you are doing is over my head.

Ken has pretty much listed all his changes out on his forum here: http://liftbars.com/phpbb3/index.php?sid=0330e5c1eb256ec894b150c09b7a1a92

It is really not all that hard to tweak the '86.5 up to 300 rwhp, especially with the 5 speeds.

porken · 07-06-2008, 11:11 AM

Quote:

Originally Posted by psychII

Well, after some fiddling, I found the culprit... an unplugged diagnostic connector.

If this was a three-pin plug, then it's the extension from the throttle switch (ground, idle, WOT). Usually this connector is falling apart, and AFAIK, is NLA.

Unplugged, the idle input will be disabled, and you'll have too much ignition advance.