Supra Idle

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

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.

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??

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.

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??

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

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..

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.

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..

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.

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?

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..

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.

$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

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

BWHAHAHAH, I would have gone to that place and whipped out $455 acting like I was going to pay for it, then tell them I could get it for $20 new, call them douchebags, and walk out. Try autozone/advanced auto, that's where I got mine and I'm pretty sure it was around $20. Thanks for the kind words, I just hope this gets solved so you can finally enjoy driving that turbo.

Well there is no autozone/advanced auto around here.. maybe not even in the country..lol
It looks like the cheapest place I could find in the city is the Toyota dealership for around $160..
It'll be a while before I get the cash to pick one up.. But when I do i'll post back and let ya know how it goes..

http://www.toyotaworld.com/
I'm pretty sure he can get you a better deal, and ship it to canada. If not there then make a WTB post on supraforums and have someone in the US buy it and send it to you. If you really want I can stop by one of those places and see if they have one in stock.

I checked the websites for Autozone, advanced auto and Toyotaworld.. and they were all inbetween $88 and $105USD for the throttle position sensor.. Which is near the same as my price of $170CND from toyota here in saskatoon..

Maybe its because you have an 88' Sup?? I believe they changed the TPS in 89', so ours isnt the same part..

No it's the same PN, I'll call up there tomorrow and see whats up cause I definetly remember it being much cheaper than $88-105.

thatd be awesome man

part number on my TPS is
89452-14050

Well I think I got a TPS on the way.. (I hope)
Guy said he'd give it to me if I paid the Shipping..
WHen I change it i'll let you know how it went

Thanks for all the help project! it doesnt look like I woulda got much help from anyone else!!

Well A guy from supraforums sent me a TPS.. didnt charge me for it, cuz he didnt need it.. Which was great.. Unfortunatly it didnt fix the problem..
I am losing my patients with this car..
What do you guys think?? should I
1) burn it and claim vandalism??
2) let it sit in the driveway and look pretty for summer??
3) or bring it in to a shop and pay outta my ass to get it fixed??

Well if you weren't way up in canada I'd come and help you out, cause I know we could figure it out then. Is there anyone localy with a turbo supra you could have come by for a day and just swap out random parts? Right now without seeing/hearing what it's doing in person I'm stumped, cause if it was something like the ECU, wiring, or most all the electronics it would be throwing codes. It's making me think maybe it's something else, how are the plugs and wires? How about the timing possibly and are all the vaccume hoses still good and connected? Sucks not being able to figure this one out, probably something simple I'm over looking too :( .

Well, just for the hell of it, I swapped out ecu's.. But it didnt do nothing... Today I noticed that every time I start it.. it idles rougher and rougher... It used to surge real smoothly but now its surging kinda rough.. giving any throttle makes it chug out and die.. My next plan of attack is to pull the intake off, see if I mised anything, and swapping all the hoses out with silicone hoses.. Because of the exhaust leak I cant hear any vacuum leaks.. so i'll replace all the hoses
I'll let ya know how it goes..

Oh.. no there isnt many supra's in my city.. and I dont know anybody with one.. None of the wreckers even have parts for it

Im starting to think that its another wiring problem as the car had earlier..

Your help is very much appreciated projectsupramk3.. This being my first supra, and my first supra problem, ive learned a lot about the car from poking around and dismantling things and from your suggestions.. Much the same.. although Ive uncovered a few other problems I hadent previously known about (missing ps hose, unhooked temp. sensors, valve cover gaskets) I still havent found the cause of my problem.. The snows all melting so now I wanna get this thing all ready for spring.. Im gonna take it to a mechanic.. I'll post the problem for future refrence incase anyone encounters the same problem.. Although im sure it'l be something small and stupid that you've told me to check.. Thanx again!

No problem, I'm just sadened that we couldn't figure this one out online, it's kind of bugging me.

Well I got good news... I had an appointment to drop the car off at 9:00am monday morning so sunday afternoon, I decided to go over everything, make sure I put it all back together.. covered up a few minor cracks in some wires (too much testing and prodding I imagine) with liquid electrical tape.. and put the battery and ecu back in.. (I always left the battery unhooked).. Monday morning.. Paid $40 to have the car towed to toi at T&T auto service (awesome import mechanics)

He phoned me at around noon and said he'd had the thing running for 45 minutes and it idled beautifully.. He never touched the thing.. Ive been driving it ever since..

Wierd no??

Ohh man that's crazy, so it was some crusty loose wires? I had forgotten all about the crispy CPS wiring problem, and the bad/crispy ground to the coil pack, was it was one of those that you patched up?

no.. I brushed some one the two wires on the cold start time switch.. and there were two tiny little cracks on the isc harness where someone used a test probe.. Im not sure if that was the problem.. I figured maybe a little moisture got between the cracks on the two isc wires..

But I must have done something somewhere.. In the last three weeks, I started it 60 times and Every single time it did the same thing.. The mechanic said he didnt want to touch anything because it was running so good.. I ripped the gasket on the ISC a week ago, I have a new one.. but im scared to put it in..lol

Either way, coulndt have done it without you
Thanx

check all of the electrical wires running to the ignition coils, it might have splits in it, if it does thaen repalce it.

im having the same problem with looping idle and stalling i have new harnes from toyota new cam position sensor new coil pack new cps and idle controle valve not installed yet. im needing any tips and also im lost on how to set the cps i check the tsrm and i still dont get how to set it. also the idle adjust screw setting information would be great

also u gotta check the grounld wire on the ingition coil and all electrical wires for cracks, the supras idle is set by the ecu not the idle screw