EGR valve VX

[dirty hands]

nope ......if you had iridiums possibly.. as they thread into position to one point in the chamber for best ignite point

I cant guarantee if you pulled the head ,did the valves.... would solve your rough idle . on your information presented

 

[kais3r]

Hmm so I did another compression test this morning after a 1 hour cruise and when I checked the spark plug it was spotless, very clean, and the compression was 180 on cylinder 2 and same on 4 so whatever it was has sorted itself out.

Btw removing Fuse 14 doesn't allow you to crank engine so I just had WOT with both inj fuses in engine bay out and the dfi disconnected.

So there's no bad compression, but even if there was, the inconsistency in the shake at idle doesn't match up with the revs, but whenever it shakes I can see the RPM dipping then raising and over compensating so it seems to be the computer fluctuating it for some reason, by about 40-50rpm.

I know it's not the IAC or TPS, I've run idle with both disconnected and does the same, EGR also had no leak.

I've got an ALDL cable now so I'll monitor some sensors and look for signs of what's making the computer fluctuate revs.

 

[dirty hands]

.Fuse 14 = bad repair manual bad . . :axe:

well there you go ... no major work needed ..you just saved yourself some bucks:w00t:

 

[kais3r]

Yeah good to know that's ok,
so just the rough idle and chirpy transmission to go then it's all A1.
Thinking of trying full synthetic ATF to see if that smooths it out.

 

[kais3r]

Did some monitoring on ALDL, only sensors that fluctuated were MAF and O2, seeing as O2s were new and are reading fairly close to the same values I'm thinking the MAF is reporting turbulent air or not reading consistently, gave it another clean and will test hooked up to airbox and without airbox to see if it stabilises.

Only other possibility is the O2 sensors are affected by flow in the exhaust, but I don't know how quickly they react and force alternate idle speeds and I'm thinking they have less say in the immediate idle revs vs the MAFS.

 

[kais3r]

Disconnected the O2 sensors, no difference there.

Still might be MAFS, is there any way to run the engine without the MAFS?
Would help to test...

Will check all over again for vac leaks...

 

[Nut Kracker]

Just unplug it and see if it makes a difference.
But.......
It will log a fault code and the ECU/PCM will probably go into default mode,
to compensate for no MAF.

That's if it already hasn't logged a code and is in working order.

 

[kais3r]

Car won't start with it disconnected ...
Should it?

 

[Nut Kracker]

It should.
The person who did my tune a few years ago,
forgot to reconnect the MAF on a 3.8 he was working on and it still ran.

He had it on the dyno, did all the stuff tuners do and after he'd finished, realised the MAF was disconnected.
He is a very experienced tuner and was very surprised that it ran so well
with it disconnected.

 

[kais3r]

No luck, still shaky with MAFS disconnected, what a PITA.

TPS
IAC
O2's
MAFS

all tried by disconnect no go.

Plugs
Leads
Coils
DFI
All fine and good spark

Compression test good and even
Full Plenum & TB Clean
No vac leaks in engine bay
Has new fuel regulator
Fuel pressure good

I take it if brake pedal goes hard after a few pumps when engine has been off a while that the brake booster is ok for leaks?

Vac tank good and had vacuum in it when I removed a plug from it so I assume this means no leaks cabin side of firewall?

Run out of things to check.
Any more ideas?