i dont believe this - Toyota Nation Forum : Toyota Car and Truck Forums

markshop · 12-03-2011, 05:56 AM

Car starts and runs full throttle and the throttle body butterfly is totally shut, cables are loose. Could the ecm do this? 1998 corolla. I changed the throttle position senser and map senser and no change.

invader · 12-03-2011, 06:41 AM

Did you try in your 8th generation Corolla section? It could be a vacuum leak somewhere between throttle body and intake manifold gasket. How are all the vacuum hoses (brake booster, etc) and PCV hoses? Open or leaking idle assist bypass valve?

hardtopte72 · 12-03-2011, 08:45 AM

That does not even sound plausible. Full throttle requires a significant amount of air and if the throttle is completely shut you would have a hard time getting that much air in the engine. Not just that but if it had a vacuum leak it would make an obvious sucking sound and not run and at least throw a P0171 for running lean since the air entering the engine would be unmetered.

Show a video of what is going on.

markshop · 12-03-2011, 10:46 AM

Sorry i put it in this section but i own a 2008 and monitor this section alot, so i wasent thinking. I am working on a 98 though. I cannot leave the key on it revs so high. doesent seem to hit a rev limiter. Can the idle air controll motor cause it to rev uncontrollable?

markshop · 12-03-2011, 10:53 AM

I also started it with the idle air control motor,throttle position senser, map senser disconnected Still reves to no end.

MasterTecInSTL · 12-03-2011, 12:45 PM

With no load on the engine it doesn't take that much air to make it rev up pretty high but no doubt about it you have an IAC stuck wide open or a major vacuum leak somewhere.

Remove the IAC and take a look at it. You might have a chunk of carbon wedged in there holding it open. You can also pinch off its hoses and cover the ports and see if it still races up. If not then a new IAC should take care of it.

***PhatRoyale*** · 12-03-2011, 03:31 PM

*moved to 8th gen forum*

markshop · 12-04-2011, 10:42 AM

Ok i think i eliminated the chance that it is the iac. I took the motor part of the iac off and manually held the shaft with the valve on it in several locations and it still revs to the top. What i mean with saying to the top is i have to turn the key on and off fast or it will rev way too fast and possibly blow a rod. I have no history on this car but we bought it at a auto auction with a blown engine meaning a blown rod. I replaced the engine and this is whats happening. I also pinched off the vacume hoses and tried it and it still does the same.

hardtopte72 · 12-05-2011, 12:01 AM

Like mastertech said this is 100% IAC valve. Unplugging the connector isn't going to do anything to a valve that is mechanically stuck open.

Also it is possible that the motor shaft has broken at the connection the valve which would explain why you can turn the motor (like when powered by the ECU) and still experience this issue.

The only way to tell this for sure is to remove the valve completely from the throttle body.

A vacuum leak that large would not let the car run. It would almost certainly die and not just that it would make an obvious sucking sound indicating it's general location.

markshop · 12-05-2011, 05:14 AM

I have removed the valve assembly from the throttle body and inspected it and the shaft is not broken.when i turn the shaft i can see the valve open the air passage and close the air passage. The valve is more like a door opening and closeing. Still stumped.

leakyseals · 12-05-2011, 08:19 AM

If you physically open and close the throttle plates at the accelerator cable what happens? I agree if the plates are closed, its taking a huge amount of air from somewhere else to not stall. A smoke test should uncover a leak that big. Maybe the intake gasket?

fishexpo101 · 12-05-2011, 11:21 AM

Quick check for a vacuum leak is to cap the throttlebody opening with a rubber block or similar (don't use your hand, incase it backfires or possibly "suctioned" to the TB opening. Same trick used on old carburated engines to help clean the jets and find leaks.

If engine still runs after capping the TB opening - then you know you have a leak somewhere between the TB and the head. As mentioned before, could be a leaking manifold gasket (at the head or behind the TB). Could also be leaking right by the TB plate pivot - can verify by wiggling the plate.

Also make sure the throttle plate is closed, even a small opening will cause it to surge like that - only air getting through should be from the IAC valve.

markshop · 12-05-2011, 11:58 AM

First off Thankyou all for trying to help me with this . I have just found the problem. I just found out the car that the engine came from was a frontal hit. I took off the intake and found a very big hole on the back side where it contacted the block. Currently waiting for a gasket now.