try unplugging the iac. if its stuck open then its letting way too much air in

IAC im not sure what that stands for sorry. or where it is.

idle air control. that controls your idle. tps doesn't do anything for idle but tell the iac when to go into neutral position. its either a brown or black plug on the bottom left on the throttle body

is it the same as the ISC that's what I see in the Haynes manual

Definitely sounds like an air leak. Check sensors, vacuum lines and gaskets for leaks.

Any ones in particular could make the car be pinned at full throttle?

I tried unplugging the ISC now the car wont turn on. It like catches but won't stay on even when I try giving it some gas.

Do you have the CAS in the right position and what is the fuel pressure set at. Check and see where you timing is at if it is advanced your idle will increase, also check the BISS screw at the front of your throttle body. Also, how did you get a 91 and tps to work with 90 they are completely different not only in connector but in design as well

Any large amount of additional air coming into the intake will make the car rev out of control. Look for loose or missing vacuum lines and check that all of the hardware on the intake / throttle body / egr is torqued down properly. Look for possible cracks in the manifold, gaskets in the right places, etc.

I just took the whole unit off the stock 1991 head and put it on the 1990 head that I took off the 1990 and put on the 1991 car. I had to because the plug was different. To sum it up I'm using a build 1990 talon as a donor to build a 1991. I had no idea so many of the connections would be different.

the engine won't stay running with isc unplugged until its warmed up. once its warmed up it'll idle

ok, thanks everyone for your help. I spent the day trying things. I did a boost leak test and I had many air leaks. I tighten everything up. I checked all vacuum line and made sure all sensors where plugged in. I is still having the same problem. When I turn the car on its like I have the gas pedal pressed all the way to the floor. Anymore thoughts or suggestions.

Dsmpagan said:

ok, thanks everyone for your help. I spent the day trying things. I did a boost leak test and I had many air leaks. I tighten everything up. I checked all vacuum line and made sure all sensors where plugged in. I is still having the same problem. When I turn the car on its like I have the gas pedal pressed all the way to the floor. Anymore thoughts or suggestions.

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Verify mechanical timing. Then ignition timing (requires a timing light)
Make sure throttle is not physically stuck open.
Major leaks usually cause the idle to stall, fooling the ECU into thinking there's more air than there really is .. at least in my experience.

Have ECM link? Make sure the idle isn't set very high. See how TPS is registering with ECU. Post a log.

Dsmpagan said:

The TPS connection was different so I took the TPS off the 1991 and put it on the 1990 head so I could plug in the cable.

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TPS is on the intake manifold , not the head. We're definitely talking about a TPS (Throttle Position Sensor)? The CAS is on the head..

I did just upgrade from ECMLink from v1 to v3. I didn't think it would be useful until I could get the car to idle. I will get it set up tomorrow and check those things.

Your right about the TPS and CAS I got my terminology mixed up. I'm learning as I go, so how do you check mechanical timing? And I followed the throttle cable and it seems to be fine no kinks or anything

Try Google for now and I'll see if I have a link saved when I get home. And yeah, most of us learn as we go . Wasn't born with what I know now and I know nothing compared to some. .

If you just upgraded to v3 make sure your injectors are dialed in properly , reference ECMlink tutorial vids if you need help doing that .

does it go to redline? if so how fast does it go up? if you have a multimeter then test the voltage from the tps. you can also clean the iac. if there's any carbon build up it'll make it stick or not work. it'd hold the butterfly open to causing a vacuum leak

OK. Enough guessing.

Quit testing the CAS and the TPS. Have nothing to do with your symptom description.

You have a bypass air problem. Period. Engine revving towards redline has nothing to do with timing either. You have uncontrolled air getting into your engine. Need to find the source of the air. Try blocking off the idle air control ports and see if the idle speed comes down. If it does, the ISC is probably stuck open. Other sources of bypass air can be intake manifold gaskets, brake booster off, etc.

All the other stuff is just checking to just check. You can take a TPS and turn it all the way to WOT in your hand and the engine won't rev, it will just run richer.

The ONLY way an engine can rev is if it can BREATHE! You engine is revving because its pulling in uncontrolled (called bypass) air. Find that and your problem is fixed.

There may also be a port mismatch between the intake/head or intake/throttle body mounting area. Spraying these areas with carb spray or propane will change the rpm and also pinpoint the areas.

kjlinwi said:

oK. Enough guessing.

Quit testing the CAS and the TPS. Have nothing to do with your symptom description.

Click to expand...

Agree the CAS and TPS have nothing to do with the issue. However I could see a timing advance, valves opening up early letting more air into the combustion chamber and causing RPM to rise as the ECU tries to compensate for lean mixture.

But fact is I'm not sure. But don't be so quick to shoot down others ideas.

OP, I would still check timing marks to make sure, then cross it off. Why not at least verify something as important as that?

http://www.dsmtuners.com/threads/pictorial-installing-timing-a-timing-belt-6bolt-2g.273973/

I am 100% sure. Engine can't run at that high an RPM without extra air. In your scenario of valves opening earlier, it will only change RPM within that idle RPM range. You can't raise RPM through timing to much over 1000 RPM. Try it for yourself sometime.

The limit on RPM is the actual throttle admitting air into the engine. If the throttle is staying closed and not flipping open with a bad spring on it (which I have seen before) then you have bypass air.

The reason you don't verify it timing, etc is becuase you don't waste your time verifying something that can't be the cause. I follow strategy based diagnostics. What you and others advocate is hunt and peck diagnostics. Check things to eliminate them with out understanding cause and effect.

Engine CAN'T rev that high without getting extra air from somewhere. Find the bypass air leak and fix the problem. Why run all over checking things just for practice?

Another thing for you to learn/understand. On start up the ECU doesn't use o2 sensors or widebands for fuel control. They have to be warmed up to operating temp by the heaters inside of them first. So the ECU will never see a lean condition to richen it up in your scenario.

On start up, engines run in open loop until the O2s are warmed up to temp. At that time, fuel control is run off of program in the software and calculated based off of baro/map and TPS, load calculations.

It's only in closed loop that fuel control by the ECU takes place using feedback from the O2s

Ok, well as long as you're "sure" hopefully that's good enough for the OP.

No. I've never been off a tooth in mechanical timing so I'm not absolutely sure of the effects. I was merely suggesting something that could increase airflow, and could have been a cause especially just after a rebuild.

No need to be an internet hero, bud. We're all just trying to help. Not like I was throwing random suggestions out there like "check the ECU", or "exhaust leak" etc. You're probably right. But it doesn't hurt to take 5 min to check your mechanical timing.

He's going to need a timing light anyway to set ignition timing after a rebuild and it sounds like he doesn't know how to do it yet. So I guess my suggestions WERE indeed helpful. Have a nice day.

I also don't presume to know what he does or doesn't know. I answered his questions and stayed on point and topic.

If you say so.

Wait! Why are you not using ECMLink to help diagnose your issue?
It can help pinpoint your issue.
Here are some resources you may find helpful:



Also, you haven't been clear about what you swapped from the 90-91. Was it literally just the head?
You would need to reuse the 91 TB, CAS, fuel rail, and ignition coils.

Ok, thank you everyone for the help so far.

I checked for air leaks again and nothing. I will check my vacuum line routing and make sure everything is fine tomorrow. The throttle body is fine. its an aftermarket one, with my Magnus intake. I never took the intake off the car when I swapped the head so it shouldn't be leaking.

I got ECMink working. I did all the basic 101 stuff. I am still having the issue.

I start the car, which takes several turns of the key, and then it catches and idles for like 5 seconds before it takes off sounds like rpm shoot up and it starts backfiring so i turn it off right away.

My tach doesn't work and I don't know why, so I cant tell if or how high the rpms go. Also it's running super rich, I can tell by the smell. I took a picture of the screen on ECMLink if it helps.

You have left out some items I have inquired about such as your head swap (ignition coils?).

I highly suggest that you create an up-to-date profile for your car. It is very difficult to help members when they start adding other items to the equation (would have been helpful to know you weren't using an OE tb).

Perhaps the check list in the ECMlink tuning forum on this site would be good to go through as well.
Found here: http://www.dsmtuners.com/threads/wa...r-receive-no-replies-from-the-wisemen.443297/

sorry i updated my profile