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#1014498 - 12/06/10 01:16 AM Stuck Throttle Over-rev Led to Knocking  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
89 pu 22re, 175k, all original internals except for TC replaced 30k ago w/ EB kit.

Twice this week the throttle stuck open in between shifts and sent the tach to 6500 before I could kill it. The throttle return spring seems ok and the stuck condition cannot be reproduced at will. I suspect the stuck throttle is a bad cable so will try replacing that. The cable is original. The casing is worn a bit near the evap canister and at another point towards the rear of the valve cover. I am located in NH and it's getting cold here. I also suspect the onset of cold weather has exposed a problem with a marginal throttle cable.

The last over-rev instance resulted in what appeared to be a cylinder miss and a valve knock. After idling for a minute the knock and miss went away. I let it cool down then went on a test drive and the engine seems to be ok. Normal power and no abnormal noises.

I suspect the valves floated and one got stuck open temporarily. Does this sound plausible or could some more severe problem be lying in wait?


From the Off-Road World

#1014499 - 12/06/10 08:38 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
Just happened again after accelerating away from a stoplight. This time I shut it down before it got above redline so no physical damage done. The over-rev happens at random and without apparent cause. There is no time to react other than kill the ignition. By the time the engine is restarted it's back to normal.

This is hard to explain, but the engine doesn't feel 'right' for a few seconds seconds after recovery. It's like there is a slight miss but then all is fine.

I am wondering if perhaps a sensor is messing up. Is it theoretically possible for a malfunctioning (e.g.) tps to direct ecu to send enough fuel to rev out the engine? Or, must the throttle plate be physically open for sufficient air to enter the intake? I'm thinking the throttle plate must be open but on the other hand with the clutch in, a super-rich condition might be tolerable.


#1014500 - 12/09/10 07:38 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
New throttle cable ($80 - ouch!) installed and so far so good. The old cable does not show any signs of binding or sticking. But, the old cable's case is worn through to the steel jacket in several spots. The engine continues to run fine so maybe I dodged one.


#1014501 - 12/11/10 06:40 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
toyrunner  Offline
Body Damage is Cool
Joined: Nov 1999
Posts: 1,049
Pasadena, CA. USA
Clean the throttle body and inspect the throttle shaft for binding(when engine is off).
Those cables do tend to randomly stick.
I use a toothbrush to clean the throttle plate and deep inside the body. You will notice an improvement.

Last edited by toyrunner; 12/11/10 06:41 PM.

1985 SR5 4Runner
eLocked with Carter Lock
4.7:1 single case
Davez Offroad twin stick

#1014502 - 12/12/10 03:03 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
engnbldr  Offline
Roll Me Over
Joined: Jun 2003
Posts: 3,576
1800 acre island at the Oregon... *****
Quote
New throttle cable ($80 - ouch!) installed and so far so good. The old cable does not show any signs of binding or sticking. But, the old cable's case is worn through to the steel jacket in several spots. The engine continues to run fine so maybe I dodged one.


>>>*If the knocking sound continues, then a cylinder leakdown test is in order. At 6500 RPM under load I would not worry too much with the 22RE, they will typically take that for brief periods. Running free is a different thing entirely.

Free running over rev situations normally affect the valve train, at 6500 RPM you would either be in or very near to a valve float situation. This can result in a valve bumping a piston, which might mean slightly bent.

Rough running after could just be excess fuel in the system that takes a few seconds to clear out, but it could also be the system hunting around to find it's own best operating point.

Note excess fuel will cause the computer to "hunt" for a period, this can cause a piston to tap until she settles down.

*I remember a smallblock we were testing once. Dual carbs, 13 to one, around 640 ponies. We threw her to full pull and the return springs popped loose and went flying.

Open headers inside a steel shop, tattletale tach went pegged and would not go any higher. Let's just say we all needed new undies before we got the coil wire yanked....*LOL**....*EB


*Beats the he** outa me!....*LOL**...

#1014503 - 12/13/10 01:33 AM Re: Stuck Throttle Over-rev Led to Knocking [Re: engnbldr]  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
Thanks for the followups. I'm gonna keep an eye on it and see what happens. Been driving it some more and it seems fine. Rev limiter seems like a good idea now.


#1014504 - 12/19/10 05:30 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
Week plus into it and no stuck throttle or abnormal engine noises despite temps into the teens, so I guess the new cable fixed it.

Couple other fixes went in around the same time. Had the temperature gauge over-shoot problem for last 1.5 years. This issue developed after a new radiator was installed. Was running a oem toyota thermostat that worked perfectly before the new rad went in. Based on forum search, there seems to be a relationship between cooling system servicing and this overshoot problem developing, but I don't know what it is. The two-stage thermostat ($40) fixed it.

The next fix was to the shifter seat bushing, replaced with Marlin parts. Shifts like new now whereas before the fix 3rd and 4th were grind city, and 5th would pop right out. Unfortunately, disassembling the shifter required 1.5 hrs of professional mechanic labor. The old rubber bushing disintegrated and prevented the lock ring from pushing down far enough to be removed.

In the end, a few relatively simple and inexpensive fixes allow me to keep my truck on the road for the foreseeable future. This forum is a great resource.


#1014505 - 03/07/11 10:08 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
Update: no issues since new throttle cable was installed until today. Feels like the butterfly is getting stuck because the pedal springs back but the feel of the pedal indicates there's no resistance from the throttle plate spring.

This time she spun to 6500 and knocked for a bit after it came back down. There is also an occasional miss at load that wasn't there before, but I think that may be related to dampness since there was a lot of heavy rain the last couple days.

I probably won't get to fixing anything for a while but will post back when and if I find anything.


#1014506 - 03/07/11 10:26 PM Re: Stuck Throttle Over-rev Led to Knocking [Re: 89PU]  
4Crawler  Offline

Web Wheeler
Joined: Jan 2000
Posts: 12,152
N. California. USA *****
Might be the old return spring is a little stretched out/weak. I have the earlier style 22RE throttle linkage and I put on a stiffer return spring:

[Linked Image]

[Linked Image]

[Linked Image]

I picked up the spring at the local hardware store, took the old one to the store and found one a little stiffer and about the same length. Has worked well, makes for a little more pedal pressure and that works well off road, where I don't get the surging throttle as you crest bumps making your foot push down on gas pedal.


#1014507 - 03/09/11 03:49 AM Re: Stuck Throttle Over-rev Led to Knocking [Re: 4Crawler]  
89PU  Offline
Getting the Wheeling Fever
Joined: Feb 2007
Posts: 38
I don't think my engine (89 22re) has the additional linkage shown in the photos. I'll double-check it tomorrow to be sure.

I'm starting to suspect the last trip to the red caused some valvetrain damage. There is what sounds like a rocker arm knock around 1500 rpm. If it was a bent valve, would the noise be consistent at all times? This noise seems to come and go. Definitely, it was there right after coming down from 6.5k. On a cold start though, no noise. I think I need to drive it some more to get a better sense of things.

Interestingly, the stuck throttle started when the weather got cold, was file all winter, and started again when the weather warmed up.


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