PCARUSA

Hi Everyone, I have a 1986.5 LHD 928 Automatic with ~138K miles. The car started 'surging' and usually stalling after I take my foot of the gas when the car reaches operating temperature. When this happens, the exhaust smells way off and I have noticed some black puffs out the exhaust at a stop light. Searching this forum suggested that I check the Throttle Position Sensor first. I checked this at the 25 pin connector at pin 3 (white) and pin 12 (white/red) and got a resistance of 1215 Ohms before depressing the accel pedal and 2013 Ohms when the throttle is cracked open. Is this OK? I removed my MAF and cleaned it up a little (I think it is the original) and put it back and took another drive. Same problem after it reaches operating temperature. My whole intake system was removed/resealed by a pro shop last summer. BTW - When I removed my MAF, I noticed a 'pool' of oil (~1.5 ounces) inside the manifold just below where the MAF fits in. I wiped this out of course. My neg. battery ground and the two small grounds above the fuse panel are good. Thanks.

AO

First off welcome!

Glad you used the search function. Sure sounds like a throttle switch issue, but as you found out, it looks like it's registering a different value from idle to partial throttle. I don't know the actual ohm figure off hand (someone else will hopefully chime in with it) but it appears that switch may not be your problem.

If the MAF is original, you're definitely on borrowed time. If you post your location, someone local to you may allow you to swap MAFs to see if that's the issue.

Hope this helps.

PCARUSA

Thanks. Glad to join this group. I still have my old '73 911T and purchased this 928 middle of last year. I think I'm hooked on them now. I live in the Redondo Beach area near Los Angeles.

TheoJ

Hi,
on a 86.5 LH ecu there should be almost zero Ohm to groundpoint and pin 3 (idle) and pin 12 (WOT) when switch activated.
Failing to make a decent contact will make the ecu think it is on pedal-control, and not in full load or idle. What you write looks like the engine is getting a rich mixture. The erractic idle behavior is explaned by a faulty idle switch failing to go to zero Ohm. Strange is that you get this funny resistance value. Normally they fail by being permanently >1Mohm or almost zero. Did you pull off the ecu connector and measure on the cable connector? You should ! Dont take readings when the ecu is connected. Maybe the ground contact is loose at the switch itself, or the plug has fallen off the switch. If no to all: take the switch off, investigate, and replace if faulty.

edit: deleted self-promotion content - RV

UKKid35

Worth mentioning that WOT starts anywhere from about 2/3 to 3/4 throttle as far as the switch is concerned.

PorKen

The test for the LH2.2 throttle switch is each pin to ground. Each pin should be infinite when off, and <10 ohms when on.

With the engine off, in a quiet place, if you open the throttle a few degrees and close it again, you can hear the faint click of the idle switch in the engine compartment, if it is engaging. The full load (WOT) switch does not make noise.

Has the idle control valve been changed? The idle rpms should not drop when you turn on the A/C, for example.

Oil in the U is normal.

PCARUSA

Hi - Thanks. I was measuring from 'pin' to 'pin' and not 'pin' to ground. I am measuring at the disconnected cable end though. Resistance from pin 3 to ground is 1 Ohm at 'idle' and 1281 Ohms when throttle is applied. Resistance from pin 12 to ground is 1216 Ohms at 'idle' and 1272 Ohms when throttle is applied. I can hear the switch click when the I move the accelerator rod about 1/4 inch. I don't think the idle control valve has been changed. The air conditioning works fine. This problem came up after I parked my car for about 20 min. and then drove away. I guess I'll startt going in and check out the switch.

PCARUSA

Hi Everyone. I just wanted to do a follow up on this problem I had a long time ago.
The 'surging' and 'stalling' and poofs of black smoke I had was the result of a bad MAF.
By the way, when the MAF goes bad, it goes bad. No warning for me. I parked the car
for about a half hour and when I came out to leave the problem started. I'm sure many
of you people already knew this but I just wanted to close out the thread I started.
Bob K.

Tony

Hey Brendan! see...your advice is being taken!

thanks for the follow up

Okv

+1.
I am sure that one day this will be very useful information, thanks.