Fast Idle (not start-up) Vacuum leak?

[CDN_Cruiser]

I continue to experience a fast idle on my truck (no fast idle on start-up - this is an ongoing thing even when the truck is warm). The truck idles around 1000RPM even when warm.

Actually the truck always feels like it's 'racing' - if I take my foot of the brake, the truck will move at a reasonable clip.

I finally had the opportunity to do a tune-up on the truck on the weekend as it was running poorly (new OEM plugs, wires, dist cap, rotor, PCV valve) and the truck runs much better, but the idle is still fast. I cleaned the TB last summer with some limited improvement.

From what I've read in prior posts some things to check seem to be:

1) Tune-up (done)
2) Clean TB (done while on truck)

3) Check throttle cable - looks like mine needs to be replaced as most of the coating is cracking, but I've tried to see if it's binding in the past without help. Is it possiblethat the cable is set for too high an idle? I unscrewed one of the cables to get to a plug - so I could see someone adjusting it for too fast an idle?

4) Air intake cracks - I unscrewed both ends and had a good look, but it seems to be ok - tope and bottom

5) Vacuum leak - how do I test this? When I pulled the hose from the PCV valve it seemed sort of loose - if the hoses are shot, can that cause a fast idle? Is there a CDan 'kit' to replace all of the relevant hoses and clips?

6) Other?

Thanks for any advice.

Cheers, Hugh

 

[landtank]

I'd disconnect all 3 cables from the TB and see how it idles. Also check the TB to make sure it closes completely by checking how the throttle plate mates to the bore when closed.

 

[fzj80kidpen]

Hugh,
I just replaced by throttle cable this weekend. Took about 30 minutes or less.
It is noticably different now. I used to feel a little snag-dead-spot in the pedal then a surge.
Now I have a nice smooth acceleration.
All you need is 10ml & 12ml wrenchs and sockets.
Disconnect from throttle body bracket and all clips.
Theres is one under the brake booster out of site about 2 inches out from the firewall.
Remove the 2 bolts holding the skinny pedal - makes it easier.
Pull it all down, pop the cable out the side of the hold - towards drivers door.
Push the new one through carefully from the inside.
Mine old one had three threads showing towards the passenger side of the throttle bracket.
I put the new one on the same way and I believe the new cable is a little tighter.
I will probably move it in to 2 threads for a little softer throttle.

As to your racing. You may need to check/adjust the accelerator cable. The one in the middle.
Others will chime in on this as you give more detail.
Interested in hearing your results from Landtank advice.

 

[fj60dave]

Have you ever adjusted the fast idle screw on the carb? This is the hard to see/find adjustment screw, and sounds like your problem. This screw is on the Aisin carb near the bottom and close to the firewall. I have to use a mirror to see this one. Adjust while the engine is running away...bring it down to 650 or so.

Vacuum leaks. Been there. Symptoms are hard starting and rough running. A single large leak is easy to find. If not obvious and your vacuum hoses are old or have never been replaced - replace them all. One by one. It has never been my experience that a vacuum leak caused high RPMs/idle.

 

[Rich]

Carb?

 

[OGBeno]

Hey Hugh:

Your problem exactly mirrors what occurred to me after doing the tune-up job today. I plan on tooling around with the throttle cable and accelerator cable to see if that might do the trick...these didn't do it for you??

Good luck and I'd definitely be interested in hearing your reports back.
Best.
-onur
Akron, OH

 

[CDN_Cruiser]

off to the garage tomorrow to do mega fluid exchange - I'm going to look at the cables as well. Im now getting some idle at around 650 and then it jumps to ~1000 after driving - so it could be a sticky cable

Cheers, hugh

 

[OGBeno]

Hey Hugh...if it helps any, I went this morning and played around a bit with the throttle cable. I loosened the throttle body side nut and the other side and fed more towareds the throttle body so it wasn't as tight as before. I tightened them up and started her up...the RPM's went down to right in spes. (+/-650RPMs).

Maybe this will help ya.

Best regards.
-onur

 

[CDN_Cruiser]

Well, the results are in and I think the problem is solved.

Over the last few weeks I've finally done a long overdue 'tune up'. I've been waiting as I wanted to do it to make sure it was done properly. I have now done the following (all OEM):

- Replace spark plugs
- Replaced wires
- Replaced distributor cap
- Replaced rotors
- Replaced PCV valve

= Runs more smoothly, but still fast idle.

Then replaced engine oil, front and rear diffs and transfer case with Amsoil synthetic fluid + new ('small good') oil filter. Front diff fluid still a bit gunked up/dark since my birf job ~ 4 months ago (this will be the third drain and flush). Rear diff looks fine after a few years, including a lot of water crossings as does the transfer case (ps why can't you access the drain plug with the OEM skid plate?!). Engine oil (synth M1) seemed to be a bit dark for a 8,000 mile change, but not too bad and given the poor performance of the engine.

I did a 3hr highway trip and some city driving and my fuel consumption is now almost 16MPG (15.8MPG, 14.98l/100KM)! Very happy. I haven't been tracking my milage very carefully , but I know that my fuel economy really sucked before doing all of this as I was really burning fuel quickly.

Oh yeah - the fast idle. All of the above did little to solve it. While I was waiting for my wife at a gas stop, I jumped out and played with the cables - I was able to slow the engine down and, sure enough, humming along nicely at the proper idle speed! So, I do need to replace the cable - very worn and likely the cause of my problems.

Edit: I'm also doing the air filter, but it was out of stock and I hadn't ordered one from CDan - that should give me the extra 0.2MPG!
Cheers, Hugh

 

[CDN_Cruiser]

Quick update - I replaced the accelerator cable tonight

(quick side note - I called Cdan for the order and mentioned I needed to replace the 'throttle cable' - he replied 'do you mean the accelerator cable?' - which I did - any other shop would have shipped me a throttle cable and I would be wondering how to install it on my accelerator!)

As others have noted the install is not difficult buy accessing the two 10mm nuts above the gas is a PITA!

My idle is still fast, so I need to play with the adjusment and try landtank's recommendation.

Is there a place in the FSM that details setting the accelerator cable? I looked and didn't see anythng.

Cheers, Hugh