rough idle help

[toomanymodz]

I'm working on a friend's 87 GN and it's got me baffled. The car is 100% stock, yet it idles rough and the idle is anywhere from 500 RPM to 850 RPM. When I start it cold, it will 'hunt' really bad and stalls a lot.

It's throwing a code 44 (lean exhaust), yet the fumes in the garage are burning my eyes out. The BLM is 150 and the Integrator is anywhere from 134 to 150, so the chip is throwing as much fuel as it can. Which makes sense because it is seeing a lean condition and it's trying to compensate.

I've gone around the engine with starter fluid checking for leaks. I've looked at every vacuum line. I haven't found any leaks thus far. I have installed a brand new MAF, plus tried one of my own known-good MAFs too. I installed new plugs, gapped them at .034, installed a new oxygen sensor. The TPS is .44 volts and the IAC counts are normal. The IAC seems to be functioning because it will maintain RPMs when I put it in gear. Fuel pressure is a tad low, 40 psi (line off) and 35 psi (line on).

Any ideas folks?

 

[dirtymax731]

Did you check your ground?

 

[toomanymodz]

Yes, I cleaned the firewall down to bare metal and re-attached the ground straps. Voltage is around 13.2

 

[dirtymax731]

Stock chip? just throwing ideas

 

[toomanymodz]

Correct, stock chip. I did order a Turbo Tweak chip and will install it tomorrow. Doubt that'll change the idle at all.

Here is some more info. When he first brought the car to me, it idled 'decent', but had zero power anything over 1/4 throttle. I discovered that someone had installed a MAF and spark plugs for a carbureted V6. Once I corrected those items, the car now runs awesome under boost, but idles much worse than before.

 

[duber3]

I had a trouble with mine that looked like yours but mine idled to high, but in gear it was OK, the TPS was always at .44, I replaced almost everything
except the TPS, guess what my problem was...the TPS, I changed it and no more high idle

 

[TexasT]

If it is that original those ancient vac lines are leaking. When I replaced mine the difference was night n day.

 

[toomanymodz]

Pretty much all of the old vac lines were replaced. Anyhow, I installed the TurboTweak chip and it ran a lot better. The idle still isn't perfect, but it's good enough for now. He's gonna pick up the car and take it home. I told him that there is a good chance the driver's side header has a leak. That would cause the issues for sure. The car is a 75k original mile 100% original Grand National. Original paint (rough) and totally rust-free other than the doors. Not sure why they have rust and the rest of the car doesn't. He may have an offer for $12k, I told him to accept the offer.

 

[toomanymodz]

This thread is worthless without pics. Here is the car. A very nice original example.

 

[GNRick]

Could be leaking at egr valve or throttle shaft seals. Or even at the intake manifold. Smoke machine will find leaks for sure.

 

[Turbo6Smackdown]

A leaking header wouldn't cause that. I'd go right for the beat down cloth intake tube looking for my leaks. I'd also wager the cal in that maf isn't super accurate either. That turbo tweak chip won't work it's best without at least a 237 fuel pressure regulator, or better yet a fully adjustable model. Hooking up a mity vac would be a good idea. Look for a steady 20" of pull.