Throttle Body Return Spring Mod...

[Andy in Pa]

So I have been dealing with a high idle problem for a while on my 89 Comanche, 4.0L 5spd.  Throttle body is VERY fresh, even bored out, IAC is clean, and seems to function fine, there are NO vacuum leaks, (all of the non-critical vacuum fittings are plugged, including the EGR), TPS is set, re-set and checked again.  My problem has been that the throttle body does not QUITE close all the way when decelerating slowly, and it will hang up at a point (usually between 1000 and 1500 rpm) as the idle goes down.  If I just pop the throttle and rev it up slightly, it closes all the way.

 

I disconnected all the throttle linkage and removed the linkage plate.  Problem went away...  TB closes fully even if I try to hang it up by closing it slowly while running.  Let it idle for a while, tried it again, still worked fine.

 

My linkage (which seems to be moving VERY smoothly, even without greasing) seems to be putting enough drag on the TB that it wasn't allowing the TB to close fully.

 

I decided to fix this in a way that I would never have to worry about it again.  I greased everything REALLY good, including the pivot linkage piece on that plate THEN added a very light throttle return spring mounted to the linkage plate.  This works great, with the added benefit of giving the gas pedal a slightly firmer and more exact feel.  I did not try just greasing the linkage before this, but truth be told, my linkage was moving quite freely, so in this case I don't think it would have helped.  I got the return spring out of the "Springs" drawer at a local Lowes.  It remains to be seen if the heat will affect the spring, but I can't imagine that it will.  

 

[87MJTIM]

I have the same issue.  When I release the gas pedal, the RPMs remain at 900-1100.  I will tap the pedal and the RPMs drop down to ~700.

 

Where did you get the spring?  What size is it?

 

It looks like you drilled a hole in the bracket.  Is the hole in the pivoting plate already there or did you drill that also?

[Pete M]

for some reason I couldn't see any of the pics in the post    but I could follow the links to facebook so I uploaded them here to the CC.   I'm sure they are out of order.

 

 

[87MJTIM]

Remember: random is an Order.

[fiatslug87]

9 minutes ago, 87MJTIM said:

Remember: random is an Order.

Random is a disorder. 

[Andy in Pa]

23 hours ago, 87MJTIM said:

I have the same issue.  When I release the gas pedal, the RPMs remain at 900-1100.  I will tap the pedal and the RPMs drop down to ~700.

 

Where did you get the spring?  What size is it?

 

It looks like you drilled a hole in the bracket.  Is the hole in the pivoting plate already there or did you drill that also?

I got the spring at Lowes out of their spring drawer.  Didn't modify it at all.  I'll see if I can get a pic of the bag it came in.  I drilled both holes.  Had to open up the hole in the bracket to be able to slip the spring end through.  The hole in the triangle bracket I just drilled to 3/16"  Its still working great too.  Logged about 400 miles on the MJ since I did this.

[boxyjeep]

Did you try tightening the spring on the throttle body by taking it apart and winding it around a few more times?

[Andy in Pa]

3 hours ago, Chargum85 said:

Did you try tightening the spring on the throttle body by taking it apart and winding it around a few more times?

No I didn't try that, because I did not have the spare parts to repair it if I broke something in that process.  I have also never heard of anyone doing that before.  I spent some time researching it too, thinking that I may be able to do that.

 

Has anyone done this?  It didn't look like it came apart easily enough to just increase this spring tension.

[Pete M]

I've only experienced sticky TBs in need of lube or broken springs.  the idea of winding one just hasn't crossed my mind.  but I'll file that away for later.