revving 3.9

Tugela

Well-known member
May 21, 2007
3,983
21
Seattle
A few months ago my wife freaked out when driving our 1993 SWB - the engine revved between 3,000 - 4,000 RPM with no feet on the pedals. She had to fight the engine with the brakes while the truck was in gear, and after shifting to neutral the engine revved even higher. She stuck her foot behind the accelerator pedal and pulled it toward her, which seemed to correct the problem.


I had a respected indie Rover shop replace the throttle cable. The performance of the truck was different afterwards. You had to depress the accelerator a ways before the throttle engaged. Over a period of weeks I progressively tightened the throttle cable tensioner knob in small increments and this improved the pedal response.


Yesterday I pulled into a gas station and while coasting in at 5-10mph the engine was still above 1,100RPM. I shifted to neutral and it jumped higher, then to park and it revved at 3,000RPM. Pulling back on the accelerator pedal did nothing.


After shutting down the engine I backed off the throttle tensioner knob a little bit. While making the adjustment I actuated the throttle by hand and the spring had resistance, it felt like it returned to its base position okay.


Reducing the tension seemed to help, but now I'm back to a little dead travel in the pedal before the throttle kicks in.


Is there something else I should inspect? I want a responsive pedal but the revving issue is troubling. The truck had been running great for several months and yesterday was the first sign of the revving issue since replacing the throttle cable.
 

rover4x4

Well-known member
Apr 21, 2004
5,145
5
36
North Carolina, Raleigh
Good job for your wife having the common sense to pull back on the accelerator pedal.

I had this happen to me a few times, as I recall the clip on the little black cruise control bellow thats attached to the throttle was getting caught. I am not sure how I fixed it but I have not had it happen again. This was like six or so years ago, maybe longer ago. My throttle cable is 27 years old and silky smooth. I know there is supposed to be a little slack in the throttle cable, I believe RAVE has a measurement for reference. There could be some build up in the throttle body, I would also think the spring on the TB could over come a bad TPS. Keep us posted.
 

p m

Administrator
Callsign: AK6PM
Apr 19, 2004
14,214
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54
La Jolla, CA
www.3rj.org
Almost never one needs to screw around with base idle. I did it once and regretted it until I sold the truck.

Clean everything around throttle cable assembly - it accumulates enough crud to provide a damper on throttle return. That includes the throttle cable itself - it needs replacement occasionally.

Speaking of throttle stop knob - I found all of them getting loose progressively; a hose clamp around one, with a tab bent around the bracket, will keep the knob in the position you want. There should be very little slack in throttle cable.
 

Tugela

Well-known member
May 21, 2007
3,983
21
Seattle
To summarize the suggestions/actions so far:

Examine clip on back of cruise control bellow - is it catching on anything?
Potential TPS issue?
Clean stepper motor - done
Clean throttle body - will do
Inspect PCV hose - they look okay, no cracks or signs of damage

Also worth recapping that prior to yesterday's gas station revving incident the truck ran great for several months post-replacement of the throttle cable, other than the pedal response issue.
 

proper4wd

Well-known member
Jun 11, 2015
65
14
boston
something is sticking or theres a very large intermittent vacuum leak. not a tps issue as it cant allow more air into the manifold on its own.
 

JohnnoK

Well-known member
Mar 19, 2017
96
1
Cape Town, South Africa
My P38 did that when I first bought it and it turned out to be the the cruise control mechanism on the plenum.

The spring was disengaged from the input lever and it sometimes wedged itself in an awkward position and jammed the throttle cable, preventing full return to idle.
 

Tugela

Well-known member
May 21, 2007
3,983
21
Seattle
I took another look at the throttle this afternoon. Upon further examination it appears that the throttle doesn't return to its position flush against the plenum. There is perhaps a millimeter or two of space between the tab that should rest on the plenum and the plenum itself. I can push the throttle tab down and it will close the gap to sit on the plenum, but the mechanism doesn't want to go all the way by itself.



Underneath the throttle is a second cable that appears to act counter to the cable leading to the accelerator pedal. This doesn't seem to have as much tension to it as it should. It feels like if it was tighter it would pull the throttle all the way down to the plenum, but it just doesn't have the oomph. I can't see where this cable leads to and there doesn't appear to be a way to adjust it via a tensioner knob like the throttle cable has. Now that I (think) I have isolated the problem, what's the trick to getting the throttle body to return to its appropriate default position when your foot is off the pedals?


Not sure if it's relevant, but there is a kind of sticky point in the travel of the accelerator pedal as you release it and the spring pushes it back to its default position. The sticky point is near the end of the pedal travel as it moves back towards the driver.
 

Tugela

Well-known member
May 21, 2007
3,983
21
Seattle
SOLUTION!

I took my Range Rover back to the shop that replaced the throttle cable. Apparently there is some connection at a junction in the throttle cable at the firewall that wasn't completely engaged. They didn't let me into the work space to watch what they were doing and the tech's explanation was unsatisfactory ("These new throttle cables are kind of funky."). Something about a spring and a connection at the firewall. I would have liked to have learned what the fix was to expand my understanding of my vehicle, but they had the truck in and out in ten minutes so otherwise no complaints.

Now the accelerator pedal has instant response, there is no sticking, no revving, the idle drops to where it should be, and everything seems to be working fine.
 

Tugela

Well-known member
May 21, 2007
3,983
21
Seattle
Yeah, I didn't say anything to the guys at the shop but I got the sense that the installation wasn't done right the first time. Still, they were prompt and responsive about making it right and I appreciate that.
 

discostew

Well-known member
Sep 14, 2010
4,606
18
Northern Illinois
clean the stepper motor and properly set the base idle
I don't think so. I bet something is hanging up in the cruise linkage. I've seen the thumbwheel for raising the idle while winching get out of position cause it's broken and hold the idle up.

Maybe if you just have someone operate the throttle while you watch from under hood you can figure out what's going on. Scary shit.
 

JohnnoK

Well-known member
Mar 19, 2017
96
1
Cape Town, South Africa
SOLUTION!

I took my Range Rover back to the shop that replaced the throttle cable. Apparently there is some connection at a junction in the throttle cable at the firewall that wasn't completely engaged. They didn't let me into the work space to watch what they were doing and the tech's explanation was unsatisfactory ("These new throttle cables are kind of funky."). Something about a spring and a connection at the firewall. I would have liked to have learned what the fix was to expand my understanding of my vehicle, but they had the truck in and out in ten minutes so otherwise no complaints.

Now the accelerator pedal has instant response, there is no sticking, no revving, the idle drops to where it should be, and everything seems to be working fine.
The cable should have a fitting at the firewall end that passes through the firewall/bulkhead and has a clip that secures it from coming out. It sounds like they bodged the installation the first time and it wasn't secured correctly/at all resulting in it possibly disengaging partially and sitting cocked off which would account for it taking up any free play and resulting in your over rev situation.