Throttle Body Binding

[porschekiller]

I am experiencing an issue with the accelerator sticking at WOT. First noticed this on the track when letting off after the straights (scary). The car just kept on going until it seems there was enough movement to jostle the mechanism loose. I've done the following:

1. Replaced throttle cable and adjusted per Bentley.
2. Adjusted accelerator pedal stop so it bottoms out slightly before the throttle stop.
3. Remove throttle body, cleaned, oiled all moving parts.
4. Removed TPS and tested. Note: may have faulty TPS, Could not get any continuity (switch to close) at WOT, even after adjustment. Adjustment done for idle properly per Bentley.

I cannot replicate the sticking throttle in the driveway. Things operate smoothly. There is smooth movement in both the pedal assembly and in actuating the throttle lever manually. The issue only seems to occur at higher speeds (4th and 5th gear on the highway). Any ideas? Seems the faulty TPS shouldn't cause things to stick at WOT. Anything else I'm missing here? Replacing throttle body?

[porschekiller]

EDIT: also greased all busing in the pedal assembly. Still no noticeable binding in there, but there is certainly side-to-side slop in the linkages.

[nando]

Has the throttle itself ever been tampered with? I mean, these cars are old.. people have done stuff to them. Some of the "big bore" throttle mods done back in the day.. were questionable. I know, I have one.

As far as the TPS, no, it's probably not causing that unless it's physically binding somehow. You will want to fix that, but all a faulty TPS should do is either cause the DME to never go to the WOT maps, or to not idle properly. It's literally just a switch, not a sensor - as in "throttle position switch". The only modes are idle, partial load, and WOT.

[porschekiller]

Update: Replaced the throttle body (and TPS) with an alternate unit. SAME ISSUE! I guess that means my problem lies in the pedal assembly somewhere. About to order and replace all bushings connected to the accelerator linkages. The pedal and linkages have a decent bit of side-to-side play, is this normal? Or should I expect this amount of play to be gone with the replacement bushings?

The weird part is that I only see this issue at 4th and 5th gear speeds at WOT. Cannot replicate in lower gears, and I cannot locate any binding whatsoever in the driveway.

[e30davie]

I dunno its hard to diagnose with text, but if it was my car i would be putting another spring on the throttle so at least it didnt try and kill me.

Your pedal should be very tight with new bushes. i replaced all mine with oem and its very nice. no real play at all.

[porschekiller]

Just wanted to wrap this up and hopefully this can help someone else out. Replaced the accelerator pedal bushings (the old ones had disintegrated), which helped remove much of the "play" in the pedal, but that still didn't solve the problem. Thanks anyway to the forum members who suggested that!

I still had a throttle sticking at WOT.

This problem was finally solved! IT WAS THE HOOD INSULATION CATCHING ON THE THROTTLE BODY. I guess at speed the airflow was forcing the insulation into the throttle body, and the inherent protruding design for the cruise control cable bracket started to wear a hole into the cloth-like material, eventually causing the "fork" to snag at WOT. Certainly a safety issue and I would recommend anyone driving these M20's to inspect their vehicles for any sort of wear that might be occurring where the hood insulation contacts the throttle body - before it escalates into the dangerous situation that I've experienced.