Supra Idle

DaMoNe6969 · #1 02-09-2004, 06:32 PM

Hey Guys, I have a 1990 Toyota Supra turbo and about a week ago when I started it up, it idled fine for a couple minutes then started to surge from about 1200 to 2200 rpm.. and its been doing it ever since.. Im not getting any codes in the ECU.. I tried cleaning the throttle body and ISC and bench tested the ISC.. i also checked the resistance of the TPS and ISC.. and they all seem to check out OK!..

I had the engine rebuilt last summer and when they lowered the engine back in they crushed a wire in the main harness.. this caused me a lot of problems, but I found it and fixed it..

Now I think that the problem may be another broken wire somewhere, I was just wondering if anyone could tell me how to check the wiring harnesses going into the tps and ISC to see if that could be the problem??

Or if there are any other suggestions as to what the problem is??
The engine runs like new for about 5 minutes, then starts surging

projectsupramk3 · #2 02-09-2004, 07:59 PM

Hmm that's strange, it definetly has something to do with the ISC or TPS, possibly the wires have been sliced/cut when the harness was crushed. Have you tried finding the ISC pinouts on the TSRM to the ECU and doing the same testing through the wires, instead of directly on the ISC and TPS. Is the ISC clicking when you shut the car off? What does it do if you rev it quickly and let off? If the ISC and wires are ok, and your sure the TPS is set correctly then it's a vaccume leak. How does she boost and run with some throttle? One other thing, get the resitances to test the AFM from the TSRM, use a DMM and that will rule out that. I doubt it's the AFM but it'd be good to rule it out for peace of mind.

DaMoNe6969 · #3 02-09-2004, 08:42 PM

I didnt bother even looking at the AFM.. I just assumed since there was no error code, then the AFM is fine.. But then I guess the same could be said about the TPS....

If I rev it up and let off quickly while its surging.. it will stall most of the time, otherwise, just return to its eratic idle...
If i put the car in drive, while its surging.. It will go relativly normally ( a little acting up when im not giving it any gas) and it boosts up normally..

Ive searched through the TSRM for info on the voltage or resistance in the wires themselves rather than the actual sensor but I havent found anything yet... Thats where Im lookin now..

Another thing... WHen the bastard put the car back together.. it looks like he broke the prongs off the BVSV so just routed a hose right from the purge to the throttlebody.. would this affect the idle??

projectsupramk3 · #4 02-09-2004, 11:04 PM

The wiring will have little to no resitance along the 3 feet of the harness, I've got the exact ohms for all gauges of wire in a book but don't really feel it's needed. Routing the charcoal canister vapor line to the intake won't hurt anything, all it does differant from the stock routing is allow gas vapors in the intake when the engine isn't warmed up yet, the BVSV closes when the engine is cold. Just check around for the obvious leaks spots (IC pipes, vacc hoses, you know) and set the TPS with a DMM if you didn't do it last time. If you just eyeballed the TPS into place I'm pretty sure that could be your problem.

DaMoNe6969 · #5 02-10-2004, 12:24 AM

I used a dmm to set the tps at closed throttle position but I didnt have thickness gauges to check the specs at an open throttle..

I found the specs on the TSRM to be a little to forgiving.. (inbetween 0.2 and 1.2) It would be hard to set the TPS out of this range..
When i installed it.. I was getting 1 ohm of resisitance between VTA and E2 at fully closed throttle

But aside from that.. When you said that you thought that could be the problem, did you mean the TPS needs to be replaced? or just adjusted?

The car ran fine for 2 months, would it just throw itself out of adjustment like that??

DaMoNe6969 · #6 02-10-2004, 12:39 AM

What do you think about unhooking the TPS and letting the car idle??

DaMoNe6969 · #7 02-18-2004, 11:07 PM

Well I set the TPS with a DMM.. It fixed my high idle problem but the car is still surging after 3 or 4 minutes of idling..

If I unhook the TPS then start the car, it wont surge it will just run in High idle.. Does that mean its fried?

Ive got a bad manifold leak.. (asshole who rebuilt the engine put the manifold back on with regular bolts and washers) That wouldnt affect the idle would it?? It makes it real hard to hear any vacuum leaks..

projectsupramk3 · #8 02-18-2004, 11:55 PM

Yes, a vacc leak would make it run like crap, although regular bolts alone wouldn't make it leak, it would have to have a bad gasket also probably. By the way did you check the ISC while you were there, is it clicking when you shut the car off? How long does it do the high idle again? Are you positive there's a vaccume leak by the way? There was an easy trick to finding the leak with some eather/starting fluid but I just can't remember it for some reason, if I do I'll post back.

DaMoNe6969 · #9 02-19-2004, 02:31 AM

Sorry, i meant it has an Exhaust manifold leak!.. my bad.. He used regular bolts (not proper studs) on the exhaust manifold, he stripped them in and they loosened up, now its leaking exhaust and its too loud for me to hear if there are any vacuum leaks anywhere else..

If i unhook the TPS, it will stay in high idle but it will not surge.. If the TPS is hooked up, it will idle fine for about 3 or 4 minutes, then start to surge...

I tested the ISC, and cleaned it.. and it does make a quiet clicking noise when I shut the car off..

This problems really got me stumped..

projectsupramk3 · #10 02-19-2004, 11:12 AM

Oh, no an exhaust leak wouldn't change idle any. So how long does it idle high, and is it doing all this when it's warm or cold? I just wanted to make sure were not talking about the cold start/high idle.

DaMoNe6969 · #11 02-19-2004, 05:23 PM

It just goes into High idle if I unhook the TPS and start it.. and it will stay in high idle (1500rpm) as long as the car is running, but will not surge...

If the TPS is hooked up, it just idles smooth at about 1000 rpm for about 3 or 4 minutes, gradually climbing to about 1500RPM.. then starts surging from 1100 to 1300 RPM like im giving it gas.. If I give it some quick throttle (to about 2000rpm) and let off, it will usually bog down and stall, or just return to surging...

I tried adjusting the TPS today while the car was running.. If I push down on the TPS a little bit (toward the passenger side) it surges as usual, if I lift up on the TPS (toward the driver side) It stops surging, but idles at 2200RPM.. Does that help you at all??

Should I just replace the TPS?

DaMoNe6969 · #12 02-19-2004, 05:25 PM

p.s. the colder it is outside, the longer it will idle smoothly for..
I tried it when it was -30C.. and it idled properly for about 6-7 minutes..
and I tried it when it was 0C and it idled properly for about 3 minutes..

projectsupramk3 · #13 02-19-2004, 09:31 PM

I'd just replace it to get it out of the way, you know your going to have to anyway and $20 isn't a big deal. You did adjust it when it was warmed up right? Cold start should idle around 1500 just as long as you posted, the colder the longer. Nothing else has been touched right? Check to make sure the yellow paint dot isn't broken on the idle screw. Definetly sounds to me like a bad/misadjusted TPS now.

DaMoNe6969 · #14 02-20-2004, 01:10 AM

$20?? I wish.. if it was $20, i would have bought 3 of them...

Toyota wants $175 for it.. (thats canadian).. So I didnt want to replace it until absolutly necessary..
But Im pretty sure thats the problem... Thanx a lot for the help man.. You Rule

DaMoNe6969 · #15 02-20-2004, 01:11 AM

theres one place in the city here that gave me a price of $455.90 for the TPS..

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