rough idle 91 lx

[BlueCoupeRedVert]

Did I miss that part?

No...i am just assuming he measured it the right way.

[Tannerm]

Ok were thinking it's a vac leak. It's not a rough idle. It's a super low idle that drops and dies after a few seconds of running. The boost gauge is showing a sporadic reading of 5 to 2 pounds of vacuum at idle. We've sprayed the piss outa all the vac lines we can find, tb, intake, etc.

[Tannerm]

Oh and it does NOT have an fmu. Has a BBK regulator.

[DON SVO]

Timing could be way off.

[Tannerm]

Well. When she's at op. Temp, she will idle without dieing. It'll drop to about 450-500 rpm after idling for a few but won't die. It cold now, it'll idle with good rpm, then it slowly dips. The computer will catch it and then dip again. Eventually die.

Denny can prolly shine more light on what I'm talking about.

[Tannerm]

Any of u cats have a smoke machine/vacuum leak detector? Make this hunt soo much damned easier!

[Denny]

The fuel pressure was at 40psi, idling with the vacuum connected. As it started surging, it would load up to 42-44psi, then correct itself or die. We pulled the vac, plugged it and started it again. The fuel was at 45-46 with no vac attached at idle. We backed it down to 32psi then reconnected the vac. The car idled at about 35-36psi with the vac connected at idle. It started surging, loaded up to about 42psi, then died. We restarted while watching the boost gauge for vac readings. Idling, it would fluctuate between 2-8 vac and it wasn't because of the surging since it was doing it before the engine started surging and wasn't in rhythm with the surges.

I'm thinking vacuum leak at this point since it never gets in a decent range and never stops fluctuating. We did screw with the IAC. We unplugged it while it was idling and it didn't effect anything. We took it apart and it was just recently cleaned. Inside the TB was just cleaned up as well. Everything looks good. The TPS was already checked and in range.

My only other concern is the recent dyno labeled with two different set of injectors. 39s are on it right now and 42s are in a box with the car. I'm wondering if the injectors were changed and not a new sampling tube in the MAF. That, and the vac leak is screwing with the FPR.

Like Tanner said, we threw carb spray all around and no signs of the vac leak. Even checked under the upper intake. Granted, the carb spray isn't an exact science, but the car defiantly has a vac leak somewhere.

[Tannerm]

What he said^^^

[Tannerm]

Seriously tho, anyone know if a shop that has a smoke machine near the flower mound area? Or a diy cheap way to this? Spraying carb cleaner seems to get me nowhere.

[Tannerm]

Ok so I got a hold of truestreet in Mckinney. They remembered this car. It came in and they found a stuck open injector. They replaced with 39lbers and retuned. The prev. Owner was gone for a week before the same low idle and surging returned (and the weak vacuum). Previous owner did not have the cash to diagnose further so he told em he would sell it. That's where I came in. If y'all hadn't figured that part out yet .

She's an absolute blast to drive. Just on cold starts and such it's a bare to keep running. Once warmed, it idles at about 900 then dips to the above stated 450. It'll intermittently surge upward in the rpm range before settling in 450rpm range again. Repeat.

I did do the poor man's smoke test (cigar smoke into vacuum line). Only smoke that protruded was out of the EGR. Even then I only got it to do this once. I about hyperventilated.

[Z06killinsbf]

Yay! Soo what does this mean?

[Tannerm]

Yay! Soo what does this mean?

I have a silly fast car (for tanner) with a possible __________ problem? Lol...

[Denny]

LMFAO!!! At least you weren't vaping!

[Tannerm]

Just for shits I replaced the iac. Interesting things I noticed. With iac unplugged at wire harness, idle rpms significantly drop (expected). But when popping the throttle it recovers quickly. Where before with old or new iac (plugged in) it would slowly retract in rpm after a rev up. I still think she has a vacuum leak I can't find... just thought I'd share.

[Z06killinsbf]

Time to start replacing lines then and do the brake clean check.

I think I have a bad vac line at my FPR, when cold it'll stutter at times and last time I had the intake off it was a little funny messing with the lines.