Test for intake leak?

jrichardson · #1 07-25-2005, 10:53 PM

On a 94 PA, how do I test for an intake manifold leak along the gasket? I have sprayed carb spray all over it when it is running, and no change in the rpm. Do I need a 'heavier' oil/liquid to temporarily 'seal' the leak?

HotZ28 · #2 07-25-2005, 11:06 PM

Why do you think you have a intake leak?

jrichardson · #3 07-25-2005, 11:10 PM

High idle (2500rpm) No visible vacuum leaks (in hoses) and Mr. Mechanic said that I have a leak in my intake at the gasket. Not sure if I trust that. Just want to make sure that this is the problem before I rip into it and replace the gaskets.

HotZ28 · #4 07-26-2005, 09:30 AM

I would check the TPS first. You can not just test the TPS for voltage. The TPS has three wires. (1) black=ground (2) white=5.0 volts (3) blue=variable voltage from .5 to 4.5. You need to test for voltage at different throttle openings. You should have .45 to.5 volts at idle and you will have an upward progression with the throttle opening up to 4.5 volts at WOT. Put one lead from your volt meter to the blue wire and the other to ground (engine), and operate the throttle through the entire range. If you test more than .5 volts at idle on the blue wire you have a problem. I had a car the other day that had a broken spring in the TPS. It did not give a code, however the TPS idle voltage was at 1.2 volts and idle was at 2000 rpm!

jrichardson · #5 07-28-2005, 09:54 PM

OK. I checked the TPS as you suggested and got a reading of 1.3 at idle!!! So I'll bet you are right on the mark with your suggestion. So I bought a TPS, and started taking of the throttle body to get to the TPS, and was then stumped.

There must be some trick to get the TB off of a 94 PA? Looks like 3 nuts, but then there is a bracket on the lower nut/bolt which impedes the TB from coming off. It appears as though you have to take this bracket off, but I can't get to the additional 2 nuts because the exhaust manifold is in the way. What is the trick to take this bracket off? Do I really have to take the exhaust manifold off to get the TB off to get the TPS off? Ugggh!

HotZ28 · #6 07-28-2005, 10:11 PM

I normally use an offset screwdriver and remove the TPS without moving the throttle body. It is not easy to get to, however it can be done.

jrichardson · #7 07-28-2005, 10:45 PM

Thanks...I'll give it a shot!

jrichardson · #8 07-29-2005, 08:24 PM

I got the TPS without taking off the throttle body. Yeah! Thanks for the suggestion! So I put on the new TPS and now the idle is over 3000! Crazy! I drove it around (with the brake on) for about 10 minutes to see if maybe the PCM just needed to relearn, but to no avail. Is there any 'adjustment' on the TPS? The Haynes manual says to 'take it to a qualified mechanic' to get it adjusted (guess I'm not qualified).

I'm ready to get the gasoline and the match at this point. Already changed out the IAC earlier. Any ideas?

TIA,

Joel

HotZ28 · #9 07-29-2005, 09:36 PM

Some are adjustable and some are not, you should be able to set the voltage at idle to .45 to .5 volts. Are you sure you got the TPS arm on top of rod on the throttle linkage? Test your voltage on the blue wire again, just like you did before. If it is higher than stated above, loosen the screws and rock the TPS assembly backwards and forward to see if you can get the right voltage.

jrichardson · #10 07-29-2005, 09:50 PM

I'll give that a try. One thing I didn't do...I did not disconnect the battery for 5-10 minutes. I"ll try that also.

HotZ28 · #11 07-29-2005, 10:00 PM

It doesn’t take that long, 30-60 sec. should be enough to reset the PCM. Turn ignition on and off while the battery is disconnected to drain any residual voltage. You can reset the PCM if you like, however that is not the problem.

DrJay · #12 07-29-2005, 11:53 PM

You're a confusing guy jrichardson:
http://www.automotiveforums.com/vbul...d.php?t=432932

You should probably recheck the TPS to make sure it's within spec if disconnecting the battery doesn't work.

jonsonton · #13 07-30-2005, 12:55 PM

I have a good way to check for an intake leak. With the car running remove the PCV valve and the hose it's connected to, together. Then if you have one of those small propane torches, open the valve and point it in your valve cover. If the RPM's change, you have an intake leak.

jrichardson · #14 07-30-2005, 05:07 PM

DrJay...sorry for being confusing. You are right. I thought I tested the TPS correctly when you suggested, and I thought it tested good...which led me back to the intake manifold. Then I tested the TPS again (correctly this time) and it looked bad. Again, thanks for the original advice, sorry for being confusing.

jonsonton, interesting idea on the intake leak. I'll file this one away for later if needed.

Joel

HotZ28 · #15 07-30-2005, 06:10 PM

Just had another thought. Have you have checked your TPS installation and voltage at idle, and are they correct? This is rare, however I have seen a crack in the flexible pipe from the EGR valve cavity, to the throttle body cause a high idle also. It may have a heat sleeve-wrap on it and be hard to see the crack. Check this flexible pipe very close. Also check the EGR valve for proper operation. If you have a intake-vacuum leak bad enough to cause the engine to idle at 3000 rpm, it should be easy to find.

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