Almost two years ago I experienced slightly erratic idle, followed by stalling every time I left off the throttle, which made getting home on that drive quite tricky. But even after that the car would barely start and would only run while feeding throttle. So I swap my ISV with a local rennlister and car ran fine, so I bought a new one and all is good.

Fast forward to a week ago which was the first drive after doing headers. I had some idle hunt from 850-1200rpm. Steve at Rennsport was kind enough to help out and advised me to unplug the O2 sensor, but the problem did not change. Upon coming home with the car hot, I unplugged the ISV and the revs came down to normal. So I pull it to clean, but its pretty spotless inside, and after that I took a drive which turned bad halfway in, with stalling once more.

How often have you guys ever had to do this? To be honest I assumed that when I swapped the old one I would not have to change it for many years to come, but it has barely been two years.

Also, I don't see this as a part to be rebuilt, unless someone does do these?

 

maybe its because I am looking into vacuum issues - but do you think maybe thats your prob and the ISV is just not able to cope?

 

Barring a vacuum leak somewhere (and thats the very FIRST thing you need to check), you may have gotten a bad ISV.

Have someone smoke test the intake system to find any vacuum leaks. If none are found, check the ISV with a DVM against the factory specs.

 

What are you using to clean the ISV? And this go around did you clean it or just take it out, check it and then put it back.

 

You can also spray different areas with starter fluid.
If the engine rev's there is a vaccum leak in that area.
As old as our cars are if you have not replaced the major hoses and vaccum lines this could be the issue.

 

What would happen if you removed the ISV completely, blocked off the openings and adjusted idle using the idle set screw on the intake butterfly??

 

Gus- Your idle would be all over the place because the ecu bounces the air/fuel back and forth from about 14.2-15.2. With some chip changes to ignore o2 sensor feedback at idle, you could get away with it.

Be careful with starter fluid. I'm not that brave! Smoke machine test is relatively cheap.

 

Although it was clean I still sprayed it a bit. I used the electrical contact cleaner I had in the garage. For some reason I didn't even think about vacuum leaks. I thought perhaps the O2 was fouled from the PB blaster at first, but that turned out false. And then once the symptoms got worse I quickly assumed ISV since it was pretty much like last time, very sudden. I'l check for obvious vacuum leaks, but if not perhaps I'l make a DIY smoker.

 

Well, looks like I was too hasty to jump on the ISV. Got a hold of a known working one but no difference. As soon as engine fires up revs jump to about 1600, then settle down to 1k for a few seconds, and even few seconds later it starts to hunt from about 850 to 1400. Also tried the DME just in case but no luck.

Looks like I'm onto vacuum lines next, which should be fun considering I know nothing about them or their whereabouts on this car.

Any hints on the more probable cause? I'm hoping its not the in the back by the FPR

 

Most of the vac hoses are shown in the Parts Catalog

 

If the butterfly in the ISV spins freely and easily, it may be ok.

Cleaning should be done with carb cleaner, as it is formulated to dissolve the carbon soot known to stick up the ISV. Brake cleaner and contact cleaner are not properly formulated solvents, to clean an ISV.

The ISV is usually a very robust component.