Stumble on deceleration after tune-up

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
I recently replaced plugs (Champion copper), wires (Kingsbourne), ignition coil (Pertronix) and distributor (Pertronix) on my 1993 RRC. Had a pro Rover tech set the timing. Checked connections on all new wires.

Issue: when I release the throttle, the engine stumbles a little as the revs wind down. Once at idle the engine settles down and smooths out. Under load the engine sounds great. It's just the transition between load and idle where it runs rough.

I'd appreciate any suggestions on what might be causing this. Symptoms were not present before installing the new distributor, so I'm guessing the issue lies in that direction.
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
I recently replaced plugs (Champion copper), wires (Kingsbourne), ignition coil (Pertronix) and distributor (Pertronix) on my 1993 RRC. Had a pro Rover tech set the timing. Checked connections on all new wires.

Issue: when I release the throttle, the engine stumbles a little as the revs wind down. Once at idle the engine settles down and smooths out. Under load the engine sounds great. It's just the transition between load and idle where it runs rough.

I'd appreciate any suggestions on what might be causing this. Symptoms were not present before installing the new distributor, so I'm guessing the issue lies in that direction.

Sounds like your minimum idle isn't set right.
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
You have a rubber hose coming around the back of the plenum. It is the air tube for most of what enters the engine thru the IAC. If you pinch that off the truck should still idle. So if you have that pinched off and the thing idles like shit, turn the idle air bleed with a allen head. I think it's a 3/16th. So you will be letting more air into the throttle that the IAC doesn't control.
 

XCELLER8

Well-known member
Sep 21, 2009
249
12
You have a rubber hose coming around the back of the plenum. It is the air tube for most of what enters the engine thru the IAC. If you pinch that off the truck should still idle. So if you have that pinched off and the thing idles like shit, turn the idle air bleed with a allen head. I think it's a 3/16th. So you will be letting more air into the throttle that the IAC doesn't control.

sorry to hi-jack....but if you have one of these 3.9's....and it's idling slightly high 850-900 rpm ( code 48), and all else seems fine, no vac leaks, throttle body spotless,etc....can you use this same method to turn the base idle down ??
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
You have a rubber hose coming around the back of the plenum. It is the air tube for most of what enters the engine thru the IAC. If you pinch that off the truck should still idle. So if you have that pinched off and the thing idles like shit, turn the idle air bleed with a allen head. I think it's a 3/16th. So you will be letting more air into the throttle that the IAC doesn't control.

Thanks, I'll check that out. Just drove the truck tonight and noticed at a stop the engine was idling at about 400 rpm.
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
Not sure if this is the ultimate solution, but the problem of the engine surging at low RPM with no throttle seems to be resolved. I tightened the throttle cable tensioner a little bit. This is the black plastic knurled knob that adjusts the throttle cable near the plate. Now if I lift off the accelerator the surge is gone. Press on the brake and same thing - no surge. There may yet be another issue that this simple fix has masked, or maybe it was just a simple fix. Time will tell.
 

Blueboy

Well-known member
Apr 20, 2004
3,205
459
Back in the USA; Rockwood, PA
Mine was loose as well when looking around awhile ago. Idle wasn?t being effected yet thought maybe full throttle was so tightened it to take the slack out. Didn?t notice much difference as can?t remember the last full pedal to the metal acceleration in the Rangie.
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
The plot thickens. I was poking around this evening and noticed two things:

1. The hose leading from the throttle towards the back driver's side of the engine bay was cracked
2. That hose led to a white plastic barbed T-junction. The other hose that connects to the T had broken off the junction and was just hanging there, also cracked. I followed that hose towards the front of the engine bay and the other end was hanging in space behind the driver's headlight.

Looks like I have some hoses to replace. Am I correct that this is part of the cruise control system? In which case that wouldn't affect the idling issue. The hose from the throttle to the T-junction is obvious. Question: for the other hose leading forward off that T-junction, what does the other end connect to? I didn't see an obvious place for it in the front of the engine bay.

I wouldn't use the cruise control even if it worked, but replacing some vacuum hoses is so cheap and easy why not do it?
 

az_max

1
Apr 22, 2005
7,463
2
There should be a round black bulb under the air intake or in that general area. It's the vacuum bulb for the cruise. If your cruise doesn't work (like mine), you can cap it off. Check where the other part of the Tee goes first.
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
I got around to adjusting the base idle as described in the Rovers North instructions in post #8. I only took a short test drive, but the performance felt improved and the engine speed transitions under braking and coasting were smooth. The surging appears to be gone. More miles will reveal how things have settled out, but for now it seems better.
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
Well, now it's doing the same surge again. Guess my adjustment of base idle did not address the issue. Will keep looking.