Engine Cutting Out @1750 Idle OK

[Pb_Foot951]

After taking my car out of storage from the winter a problem has shown up that has made it undrivable. It happened the first day once and I just let is sit and cool down and it went away for a couple days. The problem has come back to stay.

The car will start and idle perfect. I can rev it up to about 1750rpm and then it shuts down and lights off again about 1300rpm. If I take my foot off the gas it will return to an idle. If I pump the gas pedal I can sometimes get it to sputter and rev past 1750, into the high r's where it seems normal. At least with no load.

I have had the plenum off looking for vacuum leaks and didn't find much. One of the speed or reference sensors may not have been plugged all the way. I just finished putting it back together last night and it still has the same problem. However, it might be to a lesser extent.

Is there a good place to cap off the vacuum going to the interior of the car? Does the gas tank vent play into this?

The car is coming out of a 2 year rebuild and I am still working out the bugs. The engine has 1200 miles on it, 200 if them this spring.

If anyone has an idea what could be causing this problem, please reply.

Thanks, John

My car is:
1986 951
Turbo S engine
ported head
AutoXXXty MAF
K27 turbo
no cat

[Pb_Foot951]

I changed the BOV and the vacuum lines and Ts in that circuit.
No success.

In am considering changing the fuel pressure regulator and dampner.

Engine will still only rev to 1750. I think it is running rich too.

[Pb_Foot951]

I was working on my car again this weekend and took it out for a couple test drives.

It will pull all 5 gears up to 1750 and shutsdown. It does not matter where the throttle is positioned. If I downshift and get the the r's over about 2500 or so it lights off and drives normally above that rpm. Lots of power.

Occasionally, the problem will clear up for 5 or 10 minutes and drive normally.

A am wondering if the the decell circuit in the DME is malfunctioning?

Thanks, John

[robm-951]

I would bet you have a bad Throttle Position Sensor (TPS). Here is the link to a test sheet for the TPS.

On yours, I bet the idle contacts are sticking, thus only proving enough fuel for the ~1700 rpm before getting to lean to run under a load. Mine did the same thing.

You can also verify this is the problem by unplugging the TPS connector. With the TPS unplugged, you should be able to drive the car, but the idle rpm will vary quite a bit. Also, I wouldn't drive it hard with it disconnected, since the dme/klr won't get a full throttle signal.

Rob

[Pb_Foot951]

Thanks to Rob,

I installed a new TPS and the problem went away. It appeared the old one was leaking oil out from around the shaft. I do not know if they are oil filled or not.

I'm back on the road and on to the next project in my restoration.

Thanks, John