[Shotimes] My sick SHO again

[Jonas Diener]

Thanks for all your suggestions regarding my last long post.

Unfortunately I still haven't got it all worked out.

The main problem is a stumble at low RPMs, especially when the engine is still cool.  It also is hard to start sometimes, and feels somewhat weak at higher RPMs -- Feels as if the spark timing is retarded.

I don't get very good fuel mileage either.  My last tank of 93 octane got me about 14MPG.

So far I have replaced (in the order listed) the inline fuel filter, CID sensor, CPS, plugs & wires (sealing the plug wells at the same time), and the DIS module.

The plugs & wires made a big difference.  It no longer misses or burns fuel in the cats.  The other things didn't seem to make any difference.

I also checked the fuel pressure at idle and under load.  It looked good.

It seems as if the air/fuel mixture is screwed up.  When it's cold, if I snap the throttle wide open at idle, it will chug and hiccup for a second or two before it revs up, sometimes even stalling.  It's not as bad when it warms up, but it's not right either.

The guy I bought it from seemed to think the MAF sensor had a problem, although he didn't elaborate as to why he thought that.  Visually it looks OK and I've re-seated the connector a couple times.

The tach on the dash has never worked since the day I bought it, which is what led me to suspect a DIS problem.

Another weirdness is that the temp gauge always reads low.  It does move, so it's not totally broken, but it never makes it above the bottom white line on the "normal" range.

I replaced both the thermostat and the sender unit to no effect.

I also dropped the Y-pipe to check for the nasty sand stuff.  While the pipe is shaped in such a way that I can't see into the cats, I shook and knocked it around a bit and no sand or other debris fell out.

Anyway, the possibilities for what's causing my stumbling problem are being narrowed down.  Right now I think it could be any of the following:

* A vacuum leak.  I've have ordered a new upper intake gasket thinking it may be leaking there.

* The butterflies for the secondary intake runners are stuck open.  I plan to clean the intake good the next time I have it off and check the butterfly operation with a vacuum pump.

* The MAF sensor is indeed screwed up.  (or the BAP sensor.)

I'm half tempted to buy an LPM as a remedy.

The computer doesn't report any meaningful codes.  Sometimes KOEO finds an IAB problem and sometimes it doesn't.  The stored codes have told me the HEGO sensors read too rich, as well as too lean.   I have yet to have it complete a KOER test without stalling (tried many times on different days at different engine temps).

I'm open to ideas...again.
-- 

the truth may be out there
but lies are in your head