2000 GT Rough idle + hesitation around 1500-2000 RPM

[Sams2000GT]

Having some sort of problem with my GT. About 2 months ago it overheated on the freeway and coolant ended up going all over the engine because the radiator fan was not functioning and turning on to cool the car. That has since been fixed but I have noticed since this incident whenever it rains or is humid out the car hesitates and has a rough idle to it, normally only in the morning on the way to work. When driving it I can feel the engine miss like a plug is bad throughout all gears around 1500-2000 and 3000RPM as well. There is no CEL and when I drive it home it doesn't seem to have the issue in the evening. The problem is very sporadic and only happens some days.

The mechanic that fixed my car suggested to bring it back so he could check the spark plugs. He said since the car overheated it could have cracked the porcelain around one of the plugs. He of course wants to charge for this but I figured I would see if I could attempt to figure out what the issue is first myself.

Any ideas or tips?

 

[trinity_gt]

The mechanic might be on to something re the plugs.

Pull the COPs (coils) out of each hole and visually check each plug well for coolant/water left behind from the overheating. If there's any moisture in there it may cause a problem. Also check the COP boots themselves for contamination.

 

[GDawg]

The mechanic might be on to something re the plugs.

Pull the COPs (coils) out of each hole and visually check each plug well for coolant/water left behind from the overheating. If there's any moisture in there it may cause a problem. Also check the COP boots themselves for contamination.

Absolutely. Heck with the mechanic, pull them your self. Have a look at each one and look for individual problems. And clean any water out of the plug holes before removing them.

 

[wmburns]

FWIIW, if moisture gets into the spark plug holes and grounds out the spark, sometimes this will damage the COP insulator boot. The misfire will continue even though the moisture has been removed. If this is the case, consider replacing the COP boot insulators. Autozone (Durlast) sells a set of (8) insulators for less than the price of a single COP.

 

[jayrw]

I have a 00 GT and last year my intake manifold cracked which caused coolant to spray all over the motor, a couple of the sparkplug wells became filled with coolant causing a misfire, It was a pain getting out all of the coolant without removing the spark plugs but we managed to do it and the car has been running fine since.

 

[Deleted member 38176]

Yup, definitely a COP/plug issue. Ive had this problem in the past.

 

[Maxpowers]

I agree with the statements above. The symptoms sound exactly like a COP/plug issue.

 

[Sams2000GT]

Thanks all for the suggestions. Is the COP just held on by the one screw? If there is no moisture or coolant should I assume the COP is bad? Anyway to test the COP with a multi-meter?

 

[trinity_gt]

Yes, one screw. Once the screw is removed the COP can be removed by weaseling it past the fuel rail. (There's no need to remove the fuel rail in case you were wondering.)

The COP can be tested with an ohmmeter to provide a go/no-go test of the primary and secondary windings. However, such a test does nothing to test whether or not the COP has insulation issues. That is, a DC test might show a 0.6-ohm primary resistance and a 6Kohm secondary resistance (for instance) and you might think it's okay. However, when that coil is asked to deliver a 25,000 volt potential to a spark plug it may have an internal winding insulation problem that (a) basically shorts the HV causing much less to be delivered to the plug and (b) doesn't show up with a DC ohmmeter test.

 

[Sams2000GT]

Thanks trinity, i'll check them out this weekend