I have a vacuum leak on my 85GT, I posted a topic about, and I`m trying to fix it. Will it cause any damage to the engine or other part if I drive til I fix the problem, thank you, Al

Unlikely. You have probably been driving it that way for a while....have you seen the check engine light?

While unlikely, if the vacuum leak were to suck up some debris, then possibly some damage could result. And if the vacuum leak is for your brake booster, you want to fix it before you drive the car. The brake booster vacuum line is the fat one that comes off the passenger side of the upper intake and runs under the upper intake to a hose on the firewall.

quote Originally posted by Alain: I have a vacuum leak on my 85GT, I posted a topic about, and I`m trying to fix it. Will it cause any damage to the engine or other part if I drive til I fix the problem, thank you, Al

Depends on how bad it is. A vacuum leak causes a lean condition at idle through to a part throttle point where it is equalized. If it's bad enough it can burn valves and more likely warp/crack your exhaust manifolds from the increased exhaust temps that will result.

quote Originally posted by Joseph Upson: A vacuum leak causes a lean condition at idle ...

No ... at least not under steady idle conditions. All the ECM "knows" is intake temperature, rpm, and absolute manifold pressure, and there is no way for it to "know" whether the manifold pressure is due to throttle plate position or a vacuum leak. (The throttle position sensor is only used by the ECM when its value is changing rapidly.)

quote Originally posted by Marvin McInnis: No ... at least not under steady idle conditions. All the ECM "knows" is intake temperature, rpm, and absolute manifold pressure, and there is no way for it to "know" whether the manifold pressure is due to throttle plate position or a vacuum leak. (The throttle position sensor is only used by the ECM when its value is changing rapidly.)

I'll have to check into that because it hasn't been my experience. TPS position is registered in the datalog and I would expect the engine light at some point to set if the ecm sees an inconsistent TPS value relative to MAP value (at idle) and no vehicle speed. Not saying you're wrong, only that I've seen problems with this situation. Perhaps it also depends on the code mask as later obd I cars have several tables the Fiero does not have. Perhaps my memory is not serving me correctly but I do recall glowing manifolds with this condition.

The leak is around the throttle body and the engine light is not on. I barely drive her since I got that problem, hopefully will be fixed soon and I will go for a spin tonight with my wife, Al

quote Originally posted by Joseph Upson: Depends on how bad it is. A vacuum leak causes a lean condition at idle through to a part throttle point where it is equalized. If it's bad enough it can burn valves and more likely warp/crack your exhaust manifolds from the increased exhaust temps that will result.

I agree. Depends on how big of leak. Lean conditions raise opperating temps, overheat the exhaust and catalytic converter, raise underhood temps which can accelerate the deterioration of plastic and rubber parts.

You should get it fixed as soon as possible.

Regardless of whether the computer uses TPS versus MAP for setting codes, TPS doesn't come into play for steady-state fueling. Two completely different topics.

A throttle body on a speed-density car is basically a large driver-operated vacuum leak.

A vacuum leak such as the one at the throttle body gasket won't cause a lean condition.

That said, leaks at the intake manifold to head gasket will cause lean cylinders. The computer can't correct for differences between cylinders, even if a leak there registers on the MAP sensor in the plenum.

[This message has been edited by pmbrunelle (edited 08-01-2011).]

I tightened the tube underneath the TB and the one that connects to the EGR valve using small tie-wraps, the engine runs better and the idle is better too. I did not perform a check with TB spray on the TB to see if there any leaks but it runs better, there is no check light, there was none before. I don`t drive her often, she is stored on winters and only driven on nice sunny summer days, I hope the problem is fixed, will see, Al

You can likely pin point the leak with a machanic's stethoscope, They're really cheep and usefull to have. BTW; if don't hear it near the TB listin near the injectors. If you hear it near one of them put some automatic trans fluid on it and let it sit over night - that will swell up a dry O ring - then listen again the next day.

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