Throttle assembly question

I am checking out rough idling on my P38 and while checking the throttle assembly I was wondering if the stop on the linkage mechanism has been "modified" ie bent over ? I haven't seen another one but the image in the manual seems to suggest it is flat and not bent over as in the pics attached ?

Maybe my imagination but it doesn't look right.....

Surely having it bent that direction would increase the idle speed as it is holding the butterfly open further??!!??

Saint.V8 said:

Surely having it bent that direction would increase the idle speed as it is holding the butterfly open further??!!??

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Yes just so Ant. Throttle butterfly should be shut at idle. Idle being controlled by idle air valve.

Does indeed look like a bodge to work around an issue with the ICV. Seen similar thing done on other cars.

wammers said:

Yes just so Ant. Throttle butterfly should be shut at idle. Idle being controlled by idle air valve.

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Could be why it is lumpy...the poor idle valve is doing its nut!....either that of the idle valve is fecked, and a PO had bent the throttle butterfly stop to compenstate rather than fix the job!

EDIT: Beat me to it Doz

Agree with all the above + it may be worth removing ICV 2 small bolts and give a clean with carb cleaner or the like, just did the very same this week and cured my idle issues "cutting out whilst in any gear other than N"

Thanks for all the quick replies ! The history that came with the car suggests the ICV was changed out relatively recently. I had taken it off and it looked in good condition, very clean as was the throttle body. Your comments confirm what I thought, that a bodge had bee done to maintain higher idle revs, probably with a previous faulty ICV.

However, I have just taken off the inlet hose and checked the butterfly while the throttle linkage was on the stop. Its hard to tell exactly, but it looks to be fully closed. I have attached a photo.

I suspect another effect of the bodge is that as the spindle continues through to the TPS, so while at idle position it is now substantially offset. My ODB reader tells me throttle is open 18% at idle. I assume that the ECU compensates by applying an adaptive value ?

The idle is quite stable around 750 rpm in D and R, but rise substantially in P and N to around 1250 but this can vary. It can drop to about 1000, but after light throttle it rises again and wont drop. I would appreciate any thoughts on why this might be.

You've got to bend it back and see what happens. You can't really fix this until you know exactly what the original issue was that made them bend it.

Idle speed pre 99 should be 700 +- 20 RPM. 99 on 660 RPM. This is adjustable on diagnostics only. Idle speed should stay at this speed all the time, adjusted as loads are applied by the action of the idle air control valve. 1000 to 1250 is far too high unloaded. At that speed the torque converter has too much load on it. Straighten the throttle stop and work from that on diag.

wammers said:

Idle speed should stay at this speed all the time, adjusted as loads are applied by the action of the idle air control valve.

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Mine does idle at 700 nicely but when put into drive/reverse it drops to around 600 and stays there with no moving around. Is that normal?

Pretty sure mine does the same

jacckk said:

Mine does idle at 700 nicely but when put into drive/reverse it drops to around 600 and stays there with no moving around. Is that normal?

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If the idle is set at 700 RPM any load applied will obviously reduce that. The CPS should report the drop to the ECU and the ECU increase idle air to slightly weaken the mixture and speed up the engine to compensate. Returning it to 700 RPM. And also in the opposite direction if load is removed and idle RPM rises. That is it's purpose. Depends on year of car, 4.0 and 4.6 are the same idle speed, but pre 99 idle should be 700 +- 20 RPM after 99 660 RPM. Obviously the later system has a finer control than the earlier one. If yours is a post 99 car the idle is too high to start with.