95 LHS misfire

[teckenroth]

Engine has misfire (stumble) at idle, just off-idle (lite accel) and cruise. Don't notice it while in Park or under heavy accel. Tested all sensors and they metered out fine. Replaced plugs, plug wires, coil pack, PCM, and MAP sensor. I noticed however that the MAP sensor will give me a good voltage reading at idle, and the voltage increases when I raise the engine speed (as it should), but when I hold the throttle in position I noticed that the voltage on the meter starts to drop. This led me to believe that the MAP sensor had a leak. I replaced it and still had the same results (voltage leak-down during constant throttle). I've read other posts on the LHS and noticed a lot of comments about Intake Manifold gasket leaks. Would a leaky gasket cause the MAP to drop it's voltage signal? Would a leaking gasket also cause a rough engine but not display an error code?

Thanks to all for your help.

Timm

[AWP9521]

Originally Posted by teckenroth

I've read other posts on the LHS and noticed a lot of comments about Intake Manifold gasket leaks. Would a leaky gasket cause the MAP to drop it's voltage signal? Would a leaking gasket also cause a rough engine but not display an error code?

Thanks to all for your help.

Timm

A leaking intake manifold gasket is not just with LHS's it is usually associated with all models equipped with the 3.5 engine, in my experience it feels like a dead miss in one or two cylinders when idling in gear and under very slow movement of the car but usually smooths out at off idle and when accellerating or cruising I would very lightly spray around the gasket areas of the manifold and plenum with Carb Cleaner to check for leaks and usualy are around cylinders 5 or 6, also check all the vacuum lines for cracks or breakage as this will definitely cause rough idling. As far as it causing the MAP voltage to drop, I suppose it's possible, never tried it.

If no leaks are found you might want to try some injector cleaner in the gas tank as one might be sticking, also how long has it been since the fuel filter was last changed? That may cause a stumble or surging especially when cruising.

[teckenroth]

Thanks, I'll try the leak-check that you describe. The fuel filter was changed late last year. Ran injector cleaner through system late last year as well. I did replace one of the vacuum lines (5/8") that connects to the rear of the intake and a vacuum component located near the firewall, driver side. It was very, very soft (almost gummy). Will also check other vacuum lines as suggested.
I have noticed that the condition seems to be present during warmer months. Didn't really occur during winter months (in St.Louis, avg winter temp 45 deg)
Thanks and I'll post my findings!!

[newfie4ever]

Do you find the problem? I have a 95 LHS that showing simular problems.

Thanks

[MaTangy23]

I just posted a thread about the same problem and then i came across this one. Read my post (97 LHS fuel injectors/rough idle???) and let me know what you guys think. Im going to try some of the things you suggested. Ill let you know how i make out.