redrocket5000

Hello All,

I have a very strange issue with my 1987 Audi 5000CSTQ. I have owned the car for 14 years and it is approaching 300,000 miles. It is a great car but this current problem has me -and anyone else who has heard it -stumped.

About 8 months ago, I had a new intercooler put on the car after it was determined that one of the end caps has blown off. I got the car back and had boost like I had not had since '94 when I installed a stiffer wastegate spring. I did notice a little pinging at 1.8-1.9 bar voost so I laid off the "wwwhhhhhoooooooo!" type of driving for a while. About two weeks after the intercooler was replaced, I 'got on it' once and noticed the car continued to rev up to 6-7000 rpms when I pushed in the clutch to shift gears . I thought that it certainly had to be my imagination and I went on. About a week later, I got on it again and the car did it again only this time it stayed pegged at about 7500 rpms. I pulled over and shut the car down and restarted and drove home. By the time that I got home, the extremely high rpms on my 'all original 1987 parts' car took its toll on my turbocharger. It was blown out. :-( A different shop installed a rebuilt turbo the next day and I was back on the road.

Well, the problem remains. If I drive in any gear and floor it to the point of the engine being under boost pressure and under load, the car tachs at 7500-8000 rpms and stays there. As you can imagine , this is very scary and could cause another blown turbo , a blown engine or death to me! I have found that if I shut of the ignition immediately and switch it back on when this occurs , all is normal again.

So, some have thought that there may be a problem with the ign. switch, ISV, cruise control rod bushing o' death or crud in the throttle body but all of these have been ruled out so far.

Here is where it gets really interesting. I thought that maybe the extreme boost pressure that now exists in the system with the new intercooler and no leaks could actually cause the throttle body plate to stay open at full boost (one of the 2 springs on the throttle body that help to pull it closed is broken). To test this theory, I purchased a strong spring and attached it to the throttle housing and to the straps on the intercooler( it was strapped before it was put back in to guard against the ends popping of with the boost pressure). I drove the car with the spring in place and the high rev condition occured once again! So, I have a closed throttle (no fuel, no air) and my car is revving at 7500 rpms when boost is applied to the engine under load!


Any help would be appreciated,


Aaron Smith

UrbanAssaultAudi

have you also tried a full throttle scenario with the engine not running? having someone watch under the hood?

redrocket5000

yes. thank you.

-aaron

Tony Hoffman-4000Q

I've been thinking on this one for a couple of days, and I'll have to admit I'm a little stumped. As I read, I thought, I'll suggest this or that, then I'd read a bit farther and see that possibility eliminated.

Anyhow, one thing that comes to mind, well two really. The first is, why does your car go to 7500rpm's? The rev limiter should come in at 6500.

The second, and only thing I can come up with is, what about the dashpot that holds the throttle open for a second after letting off? What opperates it, and how far can it hold the threttle open. The shutoff procedure is what sort of points me there, that and the fact that I can't really imagine anything else causing it.

Anyhow, hope this helps, and let us know what the solution turns out to be. Just in case.....

Tony Hoffman