Reply With Quotethe computer looks for the signal of a closed throttle to turn on the idle control valve system, the wot switch takes the computer out of open loop o2 control and adjusts the mixture for power
Throttle Position Sensor question
I checked my TPS today (on an '89 525i euro M20 manual tranny) and I did not get any continuity at idle nor WOT positions on either side of the 3 pin terminal. My question is, does this have a very high impact on idling? Could it cause my car's kangarooing when I come to a stop, in 2nd gear, with my foot off the accelerator and rpm going down to 1000?
Right now, my idling surges when cold (about 900 rpm and suddenly bursts to 1500 and quickly down again to 900). When warm, it is relatively steady but kinda rough.
Can I trick the computer into reading the TPS at idle by pulling off the TPS harness and connecting the two terminals on the harness that correspond to terminals 8 and 13 on the TPS connector? I just want to see if there's a big difference in idling quality. Will I break something if I do this?
Thanks,
Philip
5-10 Grand Master
the computer looks for the signal of a closed throttle to turn on the idle control valve system, the wot switch takes the computer out of open loop o2 control and adjusts the mixture for power
all america wants is cold beer warm cat and a place to take a poop with a door on it
Grand Master
Sounds like a bad ICV. However, I think you can do the test you're suggesting with the TPS to see if it's the problem. Here's the guts of a TPS from a US spec 535i manual.
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy
Grand Master
Hmmm... what if you went WOT at, say, 1/2 throttle?
What if you had Mark program a chip where WOT was tuned for you car (cam, intake, MAF, whatever your setup might be) and the rest of the chip was the standard EAT. BUT - set the WOT to trip at 1/2 throttle instead of 3/4, so you can put it into the good power/bad emissions state most of the time, but keep it sane for emissions tests...Originally Posted by winfred
Is tampering with emissions controls illegal?
Robin
72 Chevy K10
01 E39 M5
Ok! Thanks guys. Jeff, it does sound like a bad ICV. But if we take Robin's theory, then the ICV is not kicking in at all with a bad TPS. I'll do my test tomorrow and let you guys know. Thanks again!
Did the test today. When I closed the circuit for idling, idling went down to about 600. Tried to drive it with the idle circuit closed but only for a very very short distance just to see if it kangaroos - it didn't!! Can this TPS be repaired just in case I can't get any spares here in the Philippines? How did you open the thing?
Grand Master
good work!
Bill and Winfred think you can carefully open up a TPS and blast the contacts clean with an electronics contact cleaner. Supposedly they fail when grease and oil get in them and gum up the contacts. That said, I completely destroyed my TPS cover trying to open it. The top was really glued on. Guess I'm just not as good as they are!
If the problem is the idle switch not triggering - have you tried adjusting the TPS so there's more force on the unit to close the contact? That may fix it.
I think my new TPS was about $50US - more than I expected. Have no idea what one would run in the Phillipines.
Jeff
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy
5-10 Grand Master
i replaced the micro switch for my hotrod project 245 turbo volvo because i needed to change from open to closed operation, that said the case is a bitch to open without killing it to the point you can't reassemble, the micro switch hardly ever dies it's usually the wot switch with it's open contacts that crud over, probably just needs adjusting, it should click when the throttle is fully closed, things that put it out of adjustment are dirty throttle body sticking open and somebody opening the throttle stop screw to prop open the throttle to mask a running problem
Bill and Winfred think you can carefully open up a TPS and blast the contacts clean with an electronics contact cleaner. Supposedly they fail when grease and oil get in them and gum up the contacts. That said, I completely destroyed my TPS cover trying to open it. The top was really glued on. Guess I'm just not as good as they are!
If the problem is the idle switch not triggering - have you tried adjusting the TPS so there's more force on the unit to close the contact? That may fix it.
I think my new TPS was about $50US - more than I expected. Have no idea what one would run in the Phillipines.
Jeff
all america wants is cold beer warm cat and a place to take a poop with a door on it
It works!!! You guys really helped me get through this one.
Anyway, got the thing opened (by sticking in thin strips of metal through the locks until it looked like a voodoo doll with lots of pins stuck in). Sure enough, there was a lot of crud. After cleaning the internals, the WOT circuit was already closing. Still had problems with the idle circuit though, it still wouldn't close. Tested the microswitch and it was working. After a lot of tracing with a multimeter, I finally found the culprit - one of the connectors of the microswitch was not making good contact with the terminal from the board. You couldn't tell by sight that there was no connection because the two contacts seemed to be connected but the tester said otherwise. By pushing the two contacts tightly together, I finally got continuity. Tomorrow, I plan to build up the connection by soldering the two contacts together just to make sure things are tight; then reassemble and reconnect everything. I'll let you know how she runs! Thanks again guys!
No more kangarooing! Also, stomp test now works! Thanks again!
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