Just put up this 1989 supra turbo. Engine has a problem where the idle keeps jumping from 1000-3000 constantly. I have no idea what to do. I thought it could be a vacuum leak so I checked all the hoses. Found some loose ones and took care of them. Put everything back together but the same issue is still there. What now?
idle jumping? keeps moving from 1000-3000
- Thread starter Prince
- Start date
Generally a surging idle like that comes from a large air leak. What were you doing prior to this problem. And what did you have apart when you "Put everything back together?".
SupraSean;1956990 said:
Not always.. Go out on your car and purposely make a vacuum leak, idle just raises due to raised fuel pressure.
OP, check your ISCV.
Clamp off the hose going to isc with a pair of needle nose vice grips. If the idle is stable then problem could be the isc.
Thought it sounded like what happens when you check fuel cut RPM, but 3,000 RPM is too high. On my tach, it looks more like 2,000 RPM (Though it's supposed to be 1,600) If your TPS is properly adjusted and working, it should hit FCO at 1,600 RPM. The RPMs would drop to about 1,200, then fuel gets turned back on, and they start going back up again.
So assuming that this is what's happening (Rev to FCO, drop to fuel return, repeat) then the only way this happens is if you're getting air into the intake manifold, and the ECU is adding fuel. For the time being, assume that it's metered air entering the manifold, since the ECU isn't starving it.
Check the ISC valve. If it's working, then you can rule that out.
Check the TPS. I believe that it could be installed such that it doesn't let the throttle body close.
Or, just check the whole TB.
If instead there's enough cold start enrichment happening, and it's UNmetered air entering the intake manifold, then there's quite a lot of it. It won't be a little vacuum hose somewhere. I can think of maybe 3 places that are big enough to cause that. Cold start injector, (Though so much for enrichment!) EGR valve opening, Brake booster line. Oh, and maybe the big vacuum port on the front of the intake manifold. Aside from that, maybe a crack in the manifold casting itself. My point here being that if it's any of these things, it should be very obvious. It takes more than a little air to rev the engine to 3000 RPM.
Edit: PCV could allow in a good amount of air, possibly even metered if the hoses are connected wrong, or your TB has failed in interesting ways.
So assuming that this is what's happening (Rev to FCO, drop to fuel return, repeat) then the only way this happens is if you're getting air into the intake manifold, and the ECU is adding fuel. For the time being, assume that it's metered air entering the manifold, since the ECU isn't starving it.
Check the ISC valve. If it's working, then you can rule that out.
Check the TPS. I believe that it could be installed such that it doesn't let the throttle body close.
Or, just check the whole TB.
If instead there's enough cold start enrichment happening, and it's UNmetered air entering the intake manifold, then there's quite a lot of it. It won't be a little vacuum hose somewhere. I can think of maybe 3 places that are big enough to cause that. Cold start injector, (Though so much for enrichment!) EGR valve opening, Brake booster line. Oh, and maybe the big vacuum port on the front of the intake manifold. Aside from that, maybe a crack in the manifold casting itself. My point here being that if it's any of these things, it should be very obvious. It takes more than a little air to rev the engine to 3000 RPM.
Edit: PCV could allow in a good amount of air, possibly even metered if the hoses are connected wrong, or your TB has failed in interesting ways.
super51fan;1958405 said:
I'd like to but it's beyond salvaging. Don't think it matters anyway cuz the OP never came back. I'll reiterate a couple of things I've said many times though:
1) A bad ISCV is no different than one that's unplugged. Neither will cause his symptom.
2) Pirate air does not increase idle speed on L Type EFI systems. Never has, never will.
Dan_Gyoba;1958413 said:
Little known fact I suppose, but the fuel cut rpm setpoint is coolant temperature sensitive and can be as high as 2700 rpm at -20C.
Thanks Pi. Learned something new today. If fuel return still at 1,200 then?
So if the ECU coolant temp sensor is unplugged, and there is metered air getting into the manifold while the TPS IDL is connected to E2, that would cause the described symptom, would it not?
So if the ECU coolant temp sensor is unplugged, and there is metered air getting into the manifold while the TPS IDL is connected to E2, that would cause the described symptom, would it not?
The fuel turn on rpm is always 400 rpm lower than the turn off rpm.
If the ECT sensor is unplugged, the default temperature of 80C will be used, which would give a 1600 rpm setpoint.
If the ECT sensor is unplugged, the default temperature of 80C will be used, which would give a 1600 rpm setpoint.
jetjock;1958458 said:
Not sure I agree with that. I had a dead ISCV on my 2JZ manifold (on my 7M). ISCV was seized open and the idle would surge exactly as the OP described. New ISCV completely cured the problem. Broken vs. unplugged ISCV all depends on the position of the plunger.
A sample of one that only proves there's likely something else wrong with your engine. On a stock 7M try it: shut the engine off and let the valve step full open. Unplug then restart. Then try different positions. All the valve does is vary the amount of metered bypass air. If everything else is working position won't matter other than rpm. And remember, the pintle is continually stepping closed from a cold start as the coolant warms. Why doesn't that cause surging idle? Lastly, someone with your background should know better than to make such a connection between the two events.