Idle surge

[Kevin Amstutz1]

Reached an impasse. This is my wife's GXP and the one I pulled the engine to R&R the oil manifold plate. No codes but it has an Idle surge. I performed a injector cutout test with my Tech II and all injectors cut out with a noticeable reduction in RPM. Viewed the misfire graph and when it surges cly 4 has the accumulated current counters, reaching the max of 64. When there is no surge the accumulated current counters reads zero.

I've checked for vacuum leaks, swapped coils and plugs, clean MAF sensor and throttle body with MAF cleaner. New coil packs on 2,4,6,8 and all new plugs.


Any ideas????

Kevin

[CMNTMXR57]

Two thoughts;

1) TPS readings. What's going on here?

2) Cat Converter issues? But that doesn't explain only one cylinder loading up.

[Kevin Amstutz1]

What should the TPS readings be? I already shipped my manuals for my next move.

[CMNTMXR57]

I don't have the stat memorized, but TPS is measured from 0 - 5 volts. 0 volts = closed. 5 volts = WOT.

So for idling, it should be somewhere less than or around 1 volt and be steady.

There are three circuits on a TPS. One supply voltage, one a ground, and one the actual voltage of the sensor.

Supply should be ~5v
Ground should be grounding
The actual is the actual blade/throttle position.

If you have a bad ground, and or you see that actual bouncing around... That might steer you somewhere.

[Kevin Amstutz1]

TP - 0%
TP - .55 at idle (Surging)
IAC goes from 50-108 counts
MAF goes from 0-12 g/s
Engine load 31-57%
MAP 41-56kpa
MAP 1.06 - 2.69 volts
No codes or check engine light. Ground connections on front lower trans connected, IIRC 3e and clean.

[Kevin Amstutz1]

I've checked all of my known vacuum connections for leaks and still have an intermittent surge. Most prevalent when initialing coming to a stop and then goes away for a moment and then comes back. Again no check engine light.


Sorry it's been a while but we moved to FL and been busy at work.

Kevin

[Kevin Amstutz1]

After many checks and head scratching, I fixed the problem. It does make a difference which of the two Crank sensors goes in their mounting position. I swapped the sensors and no more surge.

Kevin