5mge engine idle/tps problem

[ringwraith]

Hey everyone, I'm new to the forums. I did search and read through a lot of threads, but couldn't find a definite answer. I purchased a project truck a couple months ago, which was an 88 4runner with a 5mge (engine wasn't complete when I bought it, so it wasn't running), and I just got it firing up last weekend. I'm running into a few issues though. First off, it idles really high. The gauge says a tad over 3k, but it could be off because I swapped in an sr5 gauge cluster from a 4cyl 4runner (did the resistor mod so it works). I have an aftermarket tach I'm gonna hook up and compare the two and adjust it if need be. Regardless how much it is off by, it still idles really high. If I just let it sit without touching the gas pedal, it will idle high for who knows how long. The second I touch the gas, however, it all changes. It will jump between 2500rpm and 3500rpm about every second. Back and forth, until I shut off the truck. I thought I narrowed it down to the tps, because when I unplugged it, the idle smoothed out (but still very high). I ordered a tps off ebay before I did enough research, only to find it didnt fit. My engine has the square tps with 6 wires, and the one I got is round with 4 wires.

So that is my problem. I'm not sure exactly what my engine is. When I bought it, I was told it came out of an 85 Cressida. However, from doing some research, the square tps were only found on the older model 5mge's? Doesn't make any sense, because the EGR valve is in the position of the 85+ year engines (doesn't interfere with the brake booster, older engines did). I can't seem to find much info on my tps, most are the 3 or 6 wire kind. I read somewhere that the 6 wire was from an auto. My truck is a manual.

I'm going to try and adjust the tps tomorrow, as it could be out of adjustment. Also to note, is the exhaust isn't complete yet on the truck. It only goes out to the downpipe just past the exhaust manifold. I'm waiting for my electric fans to get here before I dare driving it in this heat (no clutch fan, doesn't fit) to the exhaust shop. I also read the o2 sensor could be a problem. Just wanted to get some input from people who know about these 5mge's, like what to check or do, as I don't know a whole lot. Hopefully I won't be a noob for too long, but I'd really like to get this thing on the road without problems, getting kinda anxious from looking at it sitting on the driveway for the last 2 months :P Thanks!

Oh, also note that this truck sat for months/years without running, with no oilpan. We found out it was seized after we bought it, but some penetrating oil in the cylinders for a few days freed it up. Not sure if it affects anything related to this problem though.

[HansBF109]

sounds kind of like a vacuum leak(high idle), and/ or possibly incorrect timing(high idle).

[Supradad]

So many thoughts...

Air Flow Meter? What type and from what are you running it on?

What ECU is hooked up to this thing?

I know little about the trucks so I will stop here...

[ringwraith]

I took some pics of the engine and stuff, might help. I assume most of this came out of the 85 cressida, as there are a lot of other parts that came with the truck from it (steering column, big box of wires, etc.). I'm gonna see if I can find the problem tomorrow with a fresh brain.





The wiring is still looking messy because I haven't started putting the truck back together yet, still working out the problems.

[supraz]

I had similar symptoms when the Idle Air Control Valve was stuck almost totally open. This bypasses the throttle so it idles high. It seems like the ECU would cut ignition to try to drop the speed so it would cycle between 2500 and 3500 rpm. The symptoms are almost identical to a vacuum leak between the throttle body and the intake manifold. I disconnected the IAC connector and applied 12V to the IAC valve windings sequentially and was able to step the IAC valve down so that the idle speed came down to normal values. Ultimately it was the ECU drivers to the IAC that was bad in my case. When you shut the engine off you should hear the valve stepping open.

[ringwraith]

I had similar symptoms when the Idle Air Control Valve was stuck almost totally open. This bypasses the throttle so it idles high. It seems like the ECU would cut ignition to try to drop the speed so it would cycle between 2500 and 3500 rpm. The symptoms are almost identical to a vacuum leak between the throttle body and the intake manifold. I disconnected the IAC connector and applied 12V to the IAC valve windings sequentially and was able to step the IAC valve down so that the idle speed came down to normal values. Ultimately it was the ECU drivers to the IAC that was bad in my case. When you shut the engine off you should hear the valve stepping open.

Thanks for the input, I'll try that tomorrow. So did you have to replace the ECU in order to fix that then?

It's really hard to hear anything on the engine with almost no exhaust on the engine though.

[supraz]

Yes I did change the ECU, but I did check the ECU inputs to make sure that they were getting correct information first and also the IAC valve to make sure I wasn't going to waste money on the ECU if I didn't need to.

http://www.celicasupra.com/forums/sh...-Control-issue

As HansBF109 said, it sounds like an air leak. If the Idle Air Control Valve is stuck open you could troubleshoot it like a leak. Unhook the hose leading from the valve to the cross-over tube and then plug the hose. If the idle speed goes down or the motor won't start without you holding the throttle open a bit it would indicate that the idle air control valve could be the problem. If plugging the hose doesn't change the symptoms I would suspect the IAC valve is not the culprit so don't waste money on the ECU.

[1982 Dragon]

Ermmm probably dumb question but would it happen to be because of the intake pipe delete? Pretty short there.

[ringwraith]

Yes I did change the ECU, but I did check the ECU inputs to make sure that they were getting correct information first and also the IAC valve to make sure I wasn't going to waste money on the ECU if I didn't need to.

http://www.celicasupra.com/forums/sh...-Control-issue

As HansBF109 said, it sounds like an air leak. If the Idle Air Control Valve is stuck open you could troubleshoot it like a leak. Unhook the hose leading from the valve to the cross-over tube and then plug the hose. If the idle speed goes down or the motor won't start without you holding the throttle open a bit it would indicate that the idle air control valve could be the problem. If plugging the hose doesn't change the symptoms I would suspect the IAC valve is not the culprit so don't waste money on the ECU.

Ok, just tested it by clamping off the main hose from the IAC and the truck idles way down and dies if I don't give it gas, so I'd say you are right and it's stuck open. Gonna see if I can fix it, hopefully I can just clean it. The engine did sit for a long time without running.

[ringwraith]

Ok, I tried stepping it down manually like you said, following the trsm, but it didnt change the idle at all. When I tried it with the engine off, you can hear a plunging/sucking type sound of the valve moving, but it doesn't seem to close. Sounds like the part is dead :/