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TPS testing and cleaning 200 1989

Hi,

My daughter and her 89 244 auto are in the neighborhood. She has a summer job teaching ESL at a college about an hour away and it's given me a chance to explore a low idle and occasional stall at red lights that she's complained about for a couple of years.

I mailed her a used TPS when this first came up. It seemed to bench test ok, but it did not cure the fault. I had the car for a couple of hours yesterday and would like to know if I'm on the right track.

I don't have a tach, but the idle is indeed low. Neither does it produce a momentary high idle at start up. As per Bentley, I checked for continuity between pin 2 at the ECU and ground with the key out. It was inconsistent. I also disconnected the IAC at idle and there was no change in RPM.

Both of the spare switches in my junk box would click, but only showed continuity on the bench if I applied pressure against the stop with my fingers, so I set them aside and removed the TPS from my 91 that idles normally.

Putting it into her car, I now had consistent continuity at the ECU and the idle came up a bit, close to normal, but there was still the lack of momentary high idle. Disconnecting the IAC with the car running now produced a high idle, I'd guess 1000 RPM or so, and swapping the IAC from the 91 produced the same effect. Am I right in thinking the IAC is open when disconnected and it only limits the idle air when it's working ?

The car will return next week-end and I'm wondering if I should have been checking for voltage at pin 2 of the ECU with key on. It seems I've read something about that but can't find it on a search.

I'm also wondering if a the normal high idle at start up is temperature dependent making the temp sensor a suspect. Or perhaps the ECU itself, a white label 561 is misbehaving. The car is well tuned. TB is clean and it runs beautifully otherwise.

There's not much that I can find on low idle searching the BrickBoard other than an ancient post by Lucid about an experienced Swedish Volvo mechanic he knew who claimed that deposits on the intake valves can suck up extra fuel introduced at start up and negate it's effect. It's an interesting hypothesis because my daughter uses her car mainly on short trip city driving, although coming off a 3000 mile highway cruise, I'd expect the engine to be cleaned up.

Looking up TPS availability on Ebay, there's not a lot of options other that Bosch at $115. or Standard Motor Products around $50., but I was curious about this listing.

https://www.ebay.com/itm/BOSCH-0280120301-Throttle-position-sensor-for-BMW-M3-PORSCHE-VOLVO-JAGUAR-OPEL/233302074573?epid=79336336&hash=item3651e324cd:g:-WwAAOSwOgFc24Q-

This is the first I've seen of the innards of the beast. For whatever reason, I'd always thought the box was in-penetrate-able like the box that holds the vehicle speed connectors. No so, apparently. Has any one done this successfully ? Did I miss it somewhere on the BB ? I may see if I can't rehab some of my lazy units.

regards, Peter







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New TPS testing and cleaning [200][1989]
posted by  maplebones  on Sun Aug 4 10:23 CST 2019 >

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