poor idle after warm restart

[grimreaper]

what would cause a very poor idle after a warm restart? it idles off the charts lean and misses along with right above 500 rpms for idle. Once i start driving and egts increase (above 500 degrees f) it smooths out and no issues even at idle. revs fine and only area that you can notice the issue is idle right after the start.

if i let it cool off enough to go through cold start enrichment its perfectly fine. o2 is new (bad heater circuit), no codes, plugs have maybe 2000 miles on them.

i searched but the 3 letter limit has me playing with the wording to get good results...
no exhaust leaks, valves are within spec, new coolant csi time switch, timing is set per tsrm, fuel pressure is normal etc, let me know what you think or what else i can test. would the ecu's coolant temp sensor cause something like this?

dont know if this is related. After decelerating using the engine as a brake and i push the clutch in the car idles right at 500 rpms before it works its way up a bit to the normal 650 rpms. Only does this after is fully warmed up and been driven a bit.

 

[dumbo]

what would cause a very poor idle after a warm restart? it idles off the charts lean and misses along with right above 500 rpms for idle. Once i start driving and egts increase (above 500 degrees f) it smooths out and no issues even at idle. revs fine and only area that you can notice the issue is idle right after the start.

if i let it cool off enough to go through cold start enrichment its perfectly fine. o2 is new (bad heater circuit), no codes, plugs have maybe 2000 miles on them.

i searched but the 3 letter limit has me playing with the wording to get good results...
no exhaust leaks, valves are within spec, new coolant csi time switch, timing is set per tsrm, fuel pressure is normal etc, let me know what you think or what else i can test. would the ecu's coolant temp sensor cause something like this?

dont know if this is related. After decelerating using the engine as a brake and i push the clutch in the car idles right at 500 rpms before it works its way up a bit to the normal 650 rpms. Only does this after is fully warmed up and been driven a bit.

do you have the vsv hook up to the fpr?, if not i know it can cause hard starts when hot..not sure if it causes warm idleing issuses though.

 

[grimreaper]

no fpr gets vac strait from the manifold. Starts great, maybe a second or two of crank time depending on how long it cools off for. Hot restarts are perfect in regards to idle quality right after the start.

 

[jdub]

Grim - have you checked your plug wires?

What kind of plugs and what are they gapped to?

Here's a grounding mod for the igniter that may help:
http://www.supramania.com/forums/showthread.php?t=52217

 

[mk3tattoos]

wow thats a tough one!It does sounds like an ECU problem though. i hope someone can help because i almost have the same problem

 

[CyFi6]

vapor lock?

 

[grimreaper]

ill ohm test the wires, plugs are NGK bcpr7es gapped at .028. ill double check the igniter ground.

never had vapor lock, what does it do?

 

[jdub]

It's not likely you have a vapor lock problem grim.

One other thing to check is you might have a sticky ISCV...have you ever cleaned it?

 

[grimreaper]

i have not since ive had the car, carb cleaner ok?

-wires
-add ignitor and o2 grounds
-clean iscv

i should be able to get to this tonight and ill report back

 

[jdub]

You will have to remove the ISCV and disassemble it...3 screws hold the ISC motor to the housing. Carb cleaner is fine...clean the housing and the valve plunger on the motor. there's a thin o-ring that mates between the motor and housing...be careful with it. You *might* need a new gasket for the mating surface to the manifold.

There is also a check valve in the manifold flange (looks like a little mag wheel). Pay attention to it's orientation and clean it too while you are there.

 

[grimreaper]

ok ISCV and new grounds had no effect on it. Wires are newer, not orginals, but ill have to test them in the am, left the car at my old mans shop since its supposed to freeze tonight.

coils are new, ISCV has NO coolant lines hooked up (if that matters) and clicks a few times when i shut it off, ecu temp switch is new (is this worth testing by chance?) cps is new, timing is dead on, im up to test anything just let me know

 

[CyFi6]

Well if you run out of things i still think it wouldn't hurt to test your fuel pressure. After you shut off the car, it should hold. If it doesn't hold pressure it could be causing your fuel to boil in the rail. There is a one way valve on the fuel pump that holds pressure, along with the pressure regulator, but since your normal driving ratios are fine i would suspect the one way valve...if this is actually your problem.

 

[jdub]

If it doesn't hold pressure it could be causing your fuel to boil in the rail.

You are kidding ...right?
The TSRM calls for rest pressure to be 21 psi or above for at least 5 minutes. Does the fuel "boil" after this time once pressure bleeds off?...what happens to residual heat after 5 minutes? Does it just go away? Come on...get a grip.

This statement is so far out in left field it would be hilarious...the problem is this is the tech section. Keep this kind of speculative crap out.

He may be having a fuel problem, but it's not this and it's not vapor lock. Did you notice how cold outside Grim said it was?
I agree, it wouldn't hurt to test fuel pressure, but not for these reasons.

 

[grimreaper]

fuel pressure has always been what i set it at when running(base setting that is), now once the car is off, the gauge reads zero. Its tapped into the side of the aeromotive fpr. Its been like this since ive had it. Only thing i can think of is that the port i get the reading from is at the fuel line to fpr connection so no pressure from the pump = no residual pressure. I know there have been other posts with this concern but i do not know if my thinking is right or wrong. dont get the whip out jdub, i didnt mean to with hold info , ive been scratching my head on this since ive had the car, i was hoping once i corrected the other small issues things would fall into place...

fuel pump has maybe 2000 miles on it if that matters.

i wish it was hot enough to boil something, this cold sucks.:aigo:

 

[dumbo]

Could the isc valve be freezing up without coolant line hooked up?

 

[jdub]

It *should* hold pressure for 5 minutes at 21 psi or above once shut down. If it doesn't, it can cause start problems...that is not the case here.

The coolant lines are there to prevent icing...conditions are low OAT and high humidity. The TB is the primary concern for this situation.

It appears this is a lean idle condition causing a misfire. You can test the ECU temp sensor per the TSRM, but it should not cause this. If it were reading cold with a warm car, you would go rich (warm-up enrichment).

I'm beginning to suspect the AIT sensor in the AFM or the HAC sensor in the ECU. You might want to check what your O2 sensor is reading when it does this....could be that heater circuit you mentioned.

Test the plug wires 1st for proper resistance. Did you ground the igniter per that link I posted?

 

[grimreaper]

ignitor is grounded per the thread you posted, along with the o2 sensor. ill get the wires and the AIT checked this afternoon and then is there a way to test the HAC? searching shows its built into the ecu for the 89's

 

[jetjock]

Vapor would be readily apparent on the fuel gage when the symptoms are present. Have you looked? That said you really ought to fix the rest pressure problem. Rather than shooting from the hip why not do some diagnostics? It's a simple matter to watch the fuel gage or try clearing the fuel system of vapor by jumpering the pump on at the diag block for 20 seconds prior to a start to see if the problem goes away.

 

[Nick M]

Above with JJ, and back to the FPR. He was right in post number 2, just not with the name. There is a second fuel pressure up valve just for hot starts. And it is vacuum switch controlled. Toyota called it the fuel pressure up valve. The VSV is behind the alternator.

An easy check is to pull the vacuum line off the regular fuel pressure regulator. Don't forget to plug it. Because you want to do it while running. While disconnected, you will run richer. See if it runs smoother. Keep in mind, that richer will help mask poor ignition.

 

[grimreaper]

wires start at 4.8k and get less as the length shortens. AIT checks out. The fuel pressure does not change when i pinch the return line, Pump is new. CSI is not leaking. I havent pulled the fuel rail to see if the injectors leak, is there another way to check this? when i shut the car off fuel pressure isnt lost slowly, its within a second to 0psi.

My vsv is not hooked up (surprise). Seems more then a few things have been unhooked on it over the years. not my doing

The fuel pressure up VSV is active only during hot starts. It opens the FPR vacuum port to atmosphere for 60-90 seconds after the start...increasing fuel pressure to clear any vapor. It helps to smooth idle for a few minutes. After appx 60-90 seconds the FPR port is reconnected to the intake manifold. -jdub