1990 5sfe idles erratic - Toyota Nation Forum : Toyota Car and Truck Forums

int3man · 12-31-2007, 05:28 PM

Hello First time poster. Bought a 1990 GT-S , 5 speed manual, for our 16 year old daughter, from my sister. She had it serviced so we have 80,00 miles of service records. So I feel comfortable with the car. But recently it has developed a new trick. It will start from dead cold fine and operate normally until the coolant sensor kicks in that the car is at operating temperature. The idle speed then jumps to 2200 RPM and stays there, so I just checked it for fault codes; none. I disconnect the MAP sensor and the idle returns to normal speed, replaced MAP Sensor with another used one same results. I cleaned the Throttle body using a soaked rag and screwdriver. No difference, I did notice that you could hear the supplemental air going through the IDLE SPEED CONTROLLER, so I know it's not a vacuum leak being thrown at the engine. I was trained on Carb's but have learned injections courtesy of my wife's 1990 Jag.
Thanks in advance for any assistance.
Michael :-)

[thewhitegts] · 12-31-2007, 05:51 PM

Def. sounds like an IAC problem. The pintle needle valve sounds stuck open.

int3man · 12-31-2007, 07:01 PM

Hello,
I'm playing catch-up on the terms here. IAC = ???? My Haynes manual shows a ISC Idle Speed Control valve but no IAC.

Fuel Injectors were replaced at 140,000 miles. I just fed it a Fuel pump and filter.

Also does anyone know what the delay is on the Circuit Opening relay is? IS there a delay?

Thanks!

[thewhitegts] · 12-31-2007, 07:08 PM

ISC and IACV same thing, different name with some alternaitve designs mind you. Regardless, its the Idle Air Control. Sounds like you have an issue with it.

***toyomoho*** · 12-31-2007, 07:24 PM

IAC = Idle Air Control. Provides auxiliary air to control idle speed. Plastic body valve, bolts to the throttle body, has an electric powered flapper valve. The valve can be removed for cleaning, use a plastic safe cleaning product. Do a TN history search as think someone posted photos of cleaning the unit. Otherwise try a Google search. A dirty IAC valve is a common problem if the idle is varying or too high.

int3man · 01-01-2008, 06:13 PM

Well that wasn't it. Our motor has a shutter valve on the armeture for the ISC valve. I removed the Throttle Body and removed the ISC valve. The armeture has a dampener at one end and that holds the valve at a set Mid point opening. Apply voltage on one coil and close the valve, apply voltage on the other coil and it opens more.

So after all his disassembly and cleaning I now ave an idle at 3000 RPM after the motor warms up. And if I unplug the Map ad the ISC Valve I an get down to 1,000 so I don't think that it's a vacumm leak or it would never idle down. Coiuld the EGR be stuck open? That would require something to let in more air to keep it running?

Thanks in advance.
Frustrated!

Qslim · 01-01-2008, 07:37 PM

Does the idle climb gradually as temp increases or does it jump up to 3k suddenly?

int3man · 01-01-2008, 07:45 PM

Hi,
It just jumps up as soon as it hits operating Temp. So what ever the operating temp switch is kicking in is doing it?

int3man · 01-02-2008, 05:50 PM

Well that was fun,
Spoke with a local ASE mechanic, his first question was was I chasing an erratic idle speed. YUP! So it was the IDLE SPEED CONTROL VALVE. Now having said that I can't answer why it was broken. I went to the local wrecking yard and surveyed the land, I found 2, one was a 1996 with the coil removed and the other was a 1991 with the dampener and coil removed. I bought both. My 1990 coil would not fit on the 1996 part. So I took the guts out of the 1990 parts and moved the plastic Stop and the spring over to the 1991 base. I also observed that the Throttle plate had a fair amount of daylight around it, and that the bellcrank was not hitting on it's stop. So that is why the Idle bypass screw is screwed all the way down.

Once I replaced the Idles Speed Control valve with my rebuilt one it idles at 1,000 and performs fine.

So does anyone sell a remanufactured Throttle body for these cars?

Happy New Year and thanks for the assistance !!!

int3man · 01-02-2008, 06:53 PM

Well it worked fine for 20 minutes. Shut it off came inside to do a few things, posted to the group. Went back out to go to the store and it started again. Idling at 2500 RPM with no sign of stopping. The idle dipped a couple of times and that was it. This really Sucks! Either it's broken or it's not but this better then broke is for the birds!

So I'm back to open for suggestions. I'm on the correct track because if you turn off the motor at 2500 RPM's it just slowly dies, and doesn't run on or knock or anything.

Thanks Frustrated again!

Qslim · 01-02-2008, 07:45 PM

Well damn. Like you said, you are on the right track here. Sounds like the problem might be in the motor itself (from your previous post it sounds like you didn't replace the actuator itself). Here's something right out of your manual, sounds like you know what you're doing and can handle checking resistance. Another thing I've done countless times in the past with success regarding isolating the idle control mechanism (even though it might not be high-tech) is rapping on the thing with a little hammer while the system is acting up. A lot of times a little tap will set it right for a bit and let you know that the problem is there for sure.

Disconnect the ISC valve connector.

Using an Ohmmeter, measure the resistance between terminal +B and terminals ISCC and ISCO.

Reading should be 19.3 - 22.3 ohms. If not as specified, replace the ISC valve.
Reconnect the ISC valve connector

int3man · 01-02-2008, 08:48 PM

Thanks but I checked that yesterday. Fluke meter read 20.7 and 20.2 on the coils. Haven't had the chance to ask this before but what size hammer and how hard? I've always wanted to be told to hit it with a hammer.

So the consensus is I'm Screwed?
Bummer.
I'll try the hammer handle first.
Thanks!

Any other directions to look? The Throttle plate being so open might cause things grief? The idle can not go low enough to setttle things down? The butterfly stop is .120 off the setscrew. Large air gap. IDLE bypass screw screwed all the way in. The more I type the more it makes sense to me.

int3man · 01-02-2008, 10:32 PM

Well More Broth for the Stew. I let it get Dead Cold and it worked just like it did when I first started it today. Idled down to 1,000 and ran fine. So the Cold Start injector must operate for some period of time?

Did I mention that I went over the whole intake with a propane wand? No Vacuum leaks detected. Used to find a lot of chryslers that way! Cast iron cracked heat risers.

I'm going after the (Throttle body) Bellcrank with a Dial indicator tomorrow morning.

int3man · 01-04-2008, 04:47 PM

Well the saga continues. Next time if the light doesn't come on make sure it is plugged into the wall. I kept saying that the thing went to hell in a handbasket as soon as the operating temp switch was made. So I metered the Coolant temperature switch I got 4k at 60-70 F and 5 Meg at 120 deg F (should be 400 ohms). So I'm waiting for a new one. Mean time I've been driving the car with the coolant switch disconnected. Idles fine and drives fine, just the check engine light is lit. Maybe It would be cheaper to disconnect the light!

The excessive airgap in the throttle body was the vacuum dash pot that catches the throttle if you suddenly close the throttle from speed. Wil close tomorrowwith any luck and a new Coolant switch installed.

Qslim · 01-04-2008, 07:17 PM

Duh. I should have suggested that long ago. Temp sensor resistance and perceived coolant temp value by the ECU are inversely proportional, so the computer is trying to constantly get your car up to temperature. I didn't think of it originally because usually when these sensors go bad the resistance will be infinite, and this extreme of a value tricks the ecu into richening the mixture to the point of rough running and stalling in an already warm engine.
Anyway, good job. Hopefully this will do the trick.