Intermittent weird problem...annoying

[Quadcammer]

So lately the cobra has been acting up in an annoying manner.

So, half the time the car starts and drive perfectly normally. However, the other half, its been doing this.

At start up, revs drop immediately instead of holding 1000rpm and dip to 750ish or so. Vacuum is low, i.e. at 5 inches of vacuum at 800rpm cold idle.

For the most part, the car runs fine, but after a good hard pull, the idle sometimes dips, and even when it doesn't, at a hot 800rpm idle, the vacuum is like 8in/hg as opposed to the 13-14 it normally is.

I did a datalog and nothing looks out of the ordinary for the fuel trims, maf ad counts, engine load or anything else, but of course, during the datalog it was acting fine.

Anything you guys can think of? I checked for vacuum leaks and intake obstructions, blower impellar looks fine as do all the clamped connections.

Car pulls hard on full throttle but tends to break up a bit more than normal at very light throttle.

I figure since its very intermitant its gotta be an electrical problem, be it the maf, CPS, Cam sensor, etc.

Any help would be appreciated.

Thanks

 

[Brutal Metal]

when I read the first paragraph Quad I was thinking an intake vacuum leak but you said you looked??

 

[Quadcammer]

yeah unless I'm missing a split hose or something, all seems tight.

 

[01yellercobra]

Since it acts up at part throttle maybe it has something to do with the EGR? Unless you've deleted that.

 

[Quadcammer]

still have EGR.

no codes though, and how active is the EGR at idle?

I'll have to log egr flow

 

[01SVTSnake]

The IAC for the dipping idle, but should cause that much vacuum loss.

 

[01yellercobra]

still have EGR.

no codes though, and how active is the EGR at idle?

I'll have to log egr flow

I don't know. But I did find that my EGR tube wasn't tightened today. A missed step during the engine swap. Once I tightened up the fitting even my wife noticed a difference in idle and part throttle driving.

 

[brkntrxn]

A vacuum leak or something with the MAF is what I am thinking.

 

[Quadcammer]

thanks for the input guys.

My first thought was maf as well, and IAC motor duty cycle is normal from what I can tell.

I sent the info to my tuner so maybe he'll have an idea.

First non-trivial problem the car has had in probably 2 years, so not bad.

 

[NXSVTCOBRA]

try rotating your MAF 1/4 turn.

 

[Quadcammer]

I can't, the maf is built into a steel tube.

 

[NXSVTCOBRA]

I can't, the maf is built into a steel tube.

When you get on it for a while and hit the clutch the rpms dip down low then come back up correct? Has it ever shut off?