20v ST redline at startup

[tommy_t]

Hey, my engine revs to redline immediately at startup and then settles at about 4ooo after about 15 seconds. I never let it run further than that out of fear of damaging the engine.

Has anyone seen this before?

I am trying to determine if it is the VVT solenoid, IACV, or TPS sensor. Any ideas? Could it be something else? I can't find any vacuum leaks and I can't imagine a vacuum leak causing it to rev all the way to redline.


It did this once before while I was driving it and I shut off the engine and it never happened again. A week later, I started it again and it appears to be stuck in this state.

[sirdeuce]

Sticky throttle? Not sure the IACV can flow enough to redline the engine. I think the IACV is big enough for 2k-3k RPM. Check your throttle assy and linkage for binding. Look for anything that isn't supposed to be there jamming up the works, rag, wire, bolt or whatever. check the cable for smooth operation. Any kinks or short radius bends can cause binding. Disconnect the cable and, use your hand, feel for any binding or sticking with the cable as straight as possible. Take off the airbox cover and look at the throttle plates. Are they closing all the way? If not, might have some corrosion or gunk somewhere, time to clean things. Whatever you do DON'T force anything, it could make it un fixable. By hand, operate the throttle mechanism, slowly, feel for any binding or resistance. I hope the problem is one of the things I mentioned here, not some hard to get part. Good luck finding the problem.

[yoshimitsuspeed]

I agree, I don't think there is anything that could allow that much air to get in except for the throttles being held open or a big hole after the butterflies, like the ISC or brake booster port or other big port being completely disconnected. Even those I wouldn't expect to let it go to redline.

You have really let it bounce off redline for 15 seconds at a time on a cold motor?

[tommy_t]

I don't see any reason to believe that it is a sticking throttle. The throttle was closed when I checked it.

It was sitting at redline long enough for me to crank up the car, jump out of my seat, check for a sticking throttle, run back to my seat, and shut off the car. Maybe not quite 15 seconds. By the time I was about to turn off the ignition, it dropped down to 3000.

I would imagine if it was an open hose it would never drop down, but i could be wrong. I looked everywhere and could not find a bad hose.

[sirdeuce]

A big hole after the throttles? Possible, but this being a silver top, bypassing the AFM would more than likely go too lean to support redline RPM. An unmetered leak generally kills an engine. Now, if the engine is converted to MAP a large leak could likely support high RPM.
If the throttle linkage felt free when you checked it, suspect the cable. Still look for any foreign object in the linage.

[tommy_t]

Thanks for the replies.

Your answers makes me even more confused since I am sure that the throttle is closed upon startup.

I am seriously thinking about cutting my losses. I have owned this car for 5 years and dropped over $10k in it so far to get it running right, but it has only been drivable for maybe 50 miles this entire time.

[s24a]

Tommy.....

To reach redline cold you have to have three things.
1) Fuel to the engine (injectors)
2) Spark to the engine (ignition)
3) Air to the engine (throttle) - a LOT.

The engine is basically an air pump. If you restrict airflow, then the engine is starved for the oxygen needed for combustion, and the airflow meter will limit the fuel from the injectors to match the airflow off an ECU map.

So if there is a BIG air leak to the engine the the Airflow Meter is measuring, then you will get this condition.

I suggest that you take off the air plenum and using a good light look down into the individual throttles to see where they are sitting with the throttle cable removed. Then attach the cable, look for an increased opening of the plates. A difference means that the cable is pulling the throttle open and it needs to be adjusted longer. You can also check the resistance of the cable in its sheath in case it is binding.

You might also check your TPS to make sure it is seeing closed throttle under both conditions with the Idle switch closed.

If this checks out, then you need to carefully examine your IACV inlet hose to make sure it has no cracks/leaks.
But this is secondary as in my opinion the IACV cannot flow enough air to redline your engine cold on startup. Also, since its unmeasured air, the AFM would not give a lot of fuel, although in certain cold conditions there might be enough cold open loop fueling to sustain the engine running, especially if you have installed larger injectors and/or a higher pressure regulator.

If the engine as you say then drops from redline to about 3000, you might use some brake clean and spry the throttle body to head area to see if there is a change in engine tome indicating a leak.

Be judicious, as this stuff could be flammable depending on the type.

Take your time. You will find the issue to cure it.

Hank

[sirdeuce]

When you're done don't be shy, let us know what you find. So far you have two votes on the throttle mechanicals. Good luck!

Oh, another thought on the rpm drop as the engine warms. The IACV is doing it's job, as the IACV closes the engine speed goes down, points to the throttle being held open slightly. If the engine idles normally when warmed up it could be something gummed up that sticks when cold.

[yoshimitsuspeed]

Make sure the dashpot between the throttles is hooked up to a vacuum source. That dashpot holds the throttles closed. It is not enough to make it rev higher than about 2500 on it's own but combined with another issue could contribute.
Or if there is something else preventing the vacuum from going low enough to close the dashpot (Like a huge intake leak) this could make it rev even higher because it was holding the throttle open a little more. If there was just enough vacuum to start pulling it closed this could cause the idle to slowly drop as you saw.
There still has to be a massive route of air going into the motor. Sirdeuce is right though that at least most of that air has to be going through the AFM for it to stay running which takes us back to the throttles being held open or some other way of air getting around the throttle plates.

[jondee86]

Yeah... If you are running a sweep, I'll have a dollar on the dashpot adjustment
being loose and the throttle being held too far open on starting.

Cheers... jondee86

[tommy_t]

Thanks for the replies, everyone.

I'll check the dash pot vacuum tomorrow and provide an update.

[tommy_t]

Maybe it was a stuck throttle... Not sure how I would have missed that when I checked it. Maybe I was in too much of a rush due to the high RPMs....

I took you all's advice and I oiled the throttle linkage and now there is no issue.

Now I am just concerned about how much damage was done.

I noticed that my coolant reservoir is much lower than the last time I looked at it. I can't find a leak so I am worried that I may be burning coolant.

Should I be worried about a 3 inch drop in coolant in the reservoir over 2 months time or could that be accounted for by evaporation?

[sirdeuce]

If oiling seems to have fixed the problem it would be prudent to go a step further. Disassemble, clean and inspect for corrosion or galling. Yeah it's a pain in the tailpipe, but not as much of a pain finding replacement parts. The process also removes anything that could cause excessive wear and/or reintroduce the past issue. Also good for peace of mind.

Dip in coolant level can be normal, or not. The unsealed, non-pressurized reservoir allows vapor from the hot coolant to escape to the atmosphere on a regular basis. If the loss seems excessive check for the typical failure areas. Water pump weep hole and shaft and any connection in the coolant system. Any leaks will cause the loss, no matter how small. Bleed the system. If air is present it will case hot spots and vapor pockets that will over pressure the system and boil the reservoir contents releasing excessive vapor to the atmosphere.

[tommy_t]

Thanks, sirdeuce. I will give that a shot