mathetas

Just purchased a 1990 GXL from a leading area rotary shop after they had rebuilt the engine and replaced nearly everything electrical and fuel related under the hood. I took the car with approximately 200 miles on the rebuild. I knew the car had a cat problem when I got it, so I attributed a somewhat shaky idle to the faulty exhaust. However, after replacing the main catalytic converter (no exhaust leaks anywhere after replacement), the idle problem became more pronounced. Sometimes, the car would have a pulsing idle during warm up, and it would fluctuate between 1000 and 2000 RPM (oscillating). As more miles piled on the car, the idle became weaker after it was warm. Under a lift, I found a faulty vacuum line, but it didn't fix the idle. Now, the car will warm up (from cold) pretty normal, with an occassional miss every 10 seconds or so. But, as the engine becomes 'warm' after driving a few minutes, the idle drops lower and lower if the clutch is disengaged, and once it gets to 800, it wants to quit if I'm not giving it gas. Long drives equal stall at stop signs or red lights. Any ideas?

FYI: While the car was idling, sprayed some starter fluid near the back of the engine, near the firewall, and the idle cleared up for a few seconds, and then the problems quickly came back. AND... Even if I'm on the highway (3000 RPM's), the engine will miss and shake the hell out of the cockpit a couple/three times per minute. No check engine lights or dash warnings on.

Intake Leak? Vacuum Leak? Air flow sensor? Accessory Cat Backup? Uhh???

trainwreck517

iTrader: (1)

Check TPS and readjust/replace it if needed. Search for a how to.

Also it won't idle too low since engine still has low compression and being broken in.

mathetas

So... It won't idle too low... I didn't know that. "TPS" stands for (Throttle Positioning Sensor ???)... And, if the 'TPS' is replaced/fixed and is the culprit, what should I expect the car to idle at? Thanks for the reply...

Net Seven

iTrader: (5)

If you spray starter fluid to the back and it clears up, you got vacuum leak.. thats a no brainer.

mathetas

That's what I thought to begin with... but no vacuum lines were found to be loose. Therefore, do you think it could be the intake manifold that is loosing vacuum, or perhaps an o-ring around an injector... know what I mean? I just can't find a vacuum line leaking or loose. I've heard that there is some kind of machine that forces some kind of smoke through the engine and if it seeps out, there's your leak. But, I don't know if that's a full proof way to diagnose a vacuum leak or even if it's possible.

RotaryResurrection

iTrader: (8)

The only way to diagnose a vacuum leak is with a fuel type such as starter fluid. Since vacuum pulls air IN, injecting smoke or dye into the engine intake path would only pull the smoke IN to the engine, not force it OUT into the bay where you could find a problem.

Sounds like you have a vacuum leak somewhere, perhaps one of the manifold gaskets or the like.

But, series 5 NAs have never been accused of being the smoothest idling pieces of equipment in the world...I have only ever seen a few that could be considered smooth at idle.

For the time being, just bump your idle up with one of the 2 throttle body idle adjustments and go on with your business until breakin is done. Then take it back down and see what you have. IF the problem is still there, and it probably will be, take it back to the builder.

In a situation like this I would take a look at it for free, and would probably make it better, but not perfect. You can't expect this particular engine to idle perfect...summer days coming to a redlight with the a/c on could still spell a stall for you, even with everything else being okay. Also, automatics are bad to stall for no apparent reason, even when everything else is right.

This poor idle, along with OMP failure that takes out the ECU with it, are the 2 biggest pitfalls of an s5 NA, IMO.

mathetas

Well... problem fixed. I bought the car from the son of the builder (rotary specialist) - who dabbles in repairing rotaries himself. But, anyway, I called him and told him the deal. He called me back and told me his dad didn't want any part of the repair because I bought the car "AS IS". But, the son told me that he'd give the problem a shot if I'd trust him with it.

I hauled the car there (lost a transmission in a truck on the way - huge mess), and today he let me know the problem was fixed. He took the intake off and resealed it with gaskets and silicon, and replaced all the vacuum lines that weren't silicon with silicon tubing. He cut the engine on, and the problem was still there - exactly the same as before.

He removed the intake again, baffled and ready to quit, and he called his dad. His dad told him that the car had a warped intake after rebuilding the engine, so he put another one on it. And, for some reason, he couldn't quite get the idle right (it wasn't as bad then as it was now), which is why he didn't want to look at it anymore. He had the engine for over a year.

Anyway, the son took the intake back off, and out of frustration, he compulsively lifted and lowered the intake on and off the engine wondering what in the heck could be wrong. Then, he noticed a metal sound every time he struck the engine with the intake. Under the gasket, barely big enough for the eye to see, was a small nipple of metal raised above the engine where the manifold takes seat. It was part of an engine plate that's top edge articulates with the lower manifold. He then remembered that his dad had removed that part off of an '87 engine during the rebuild, as that particular part from the '90 was cracked (the plates were exactly the same size). The nipple was misarticulating the seat of the manifold, leaking vacuum, and warping the intakes.

Unfortunately, I have to pay the son for correcting his father's mistake (not cheap, either). But, to my surprise, the son told me that he has never driven a more perfect and smooth running 2nd generation engine after he fixed my car. I could tell he was very envious. So, I'm gonna cut my losses and pay him without a word - at least I get my car back running well.

mathetas

Got my car back and it runs great... After dealing with the son of the builder on the matter, I think the endeavor was worth every penny. That fella is one helluva tuner and a great guy to boot.