Random tickover
Discussion
Alright chaps.
Bit of a strange thing going on.
Had a quick blast in the wedge over the weekend. Started her up no problem. Tickover a bit low but fine when she warmed up on the drive, all normal.
Went for a run and after a a while when I slowed down the tickover had increased to around 1500!
Strange.
Carried on for a while and got back home with tickover still high.
It seems to be variable. Get it right stood still, have a blast and it changes.
Any ideas?
Bit of a strange thing going on.
Had a quick blast in the wedge over the weekend. Started her up no problem. Tickover a bit low but fine when she warmed up on the drive, all normal.
Went for a run and after a a while when I slowed down the tickover had increased to around 1500!
Strange.
Carried on for a while and got back home with tickover still high.
It seems to be variable. Get it right stood still, have a blast and it changes.
Any ideas?
“Rover Efi V8 Idle Speed Hang-up”
A common fault on the Rover Single Plenum Efi system throttle mechanism is “Idle Speed Hang-up”. Friction anywhere in the assembly is the killing factor caused variously by damage, misalignment, contamination and maladjustment. Blocked airways and air leaks are also a concern. This action program will resolve the problem.
Ensure that the accelerator cable is correctly adjusted
• Allow some free play but without undue slack. If excessively high idling speed cannot be reduced by turning the idle air adjusting screw clockwise, take the following action.
Check that the throttle plate closes fully
• Warning: Throttle must never be moved by turning the plate/disc, otherwise it will damage the delicate spindle
• The quadrant and its associated linkages are carefully adjusted during manufacture and would not normally be disturbed, except, as most systems were manufactured more than 30 years ago, incorrect fit due to worn parts is now quite common. The following actions can be taken.
• Disconnect the throttle cable from the quadrant and remove the return spring.
• Undo the quadrant securing set-screw/nut/washers and remove the quadrant from its shaft.
• Check the quadrant hub for distortion and undue wear preventing it from securely fitting the shaft.
• Check all the linkages for wear.
• If after the above actions the engine idling speed it still excessive, it may be necessary to remove the plenum chamber to check the following:
Air tight connection between plenum chamber and trumpet housing
• If unable to locate an air leak with the engine running whilst squirting some WD40 along this joint, remove the plenum chamber and check that an incomplete seal between the face of the plenum chamber and the trumpet housing is not allowing air to enter the plenum chamber along that location.
Fit of throttle disc to air intake tunnel of the plenum chamber
• There is not normally a throttle-stop adjustment screw on the original Plenum system and an airtight fit between throttle disc and the intake tunnel is required. Set quadrand mechanism and throttle cable as required to achieve this. However some retro-itted throttle assemblies do have a throttle stop adjustment screw making accurate adjustment somewhat easier. Use a torch to check the gap. A suspect disc can be changed if replacements are available, otherwise clean off all deposits and polish the edges and faces for a significant improvement.
• Use needle pliers to close the split thread of the disc fixing screws before they are removed. Make an identity mark on the disc to ensure it can fe re-fitted the right way around. Inspect edge for dents or distortion and take extreme care with any renovation of the edges.
• Check the spindle for excessive wear or distortion and replace it if required. If new item is unavailable, again, the existing spindle might be significantly improved by cleaning and polishing. The shaft provide primary bearing surfaces so polishing in that area should be minimised. Dress the slot with fine abrasive paper and needle files to remove burrs or dents and ensure that the throttle disc slides smoothly in its slot to aid re-assembly.
• Upon re-assembly, smooth operation without friction in the intake tunnels is paramount. This depends upon axial location of the disc in its slot after the retaining screws are tightened. If the disc interferes with the tunnel, slacken the fixing screws with the throttle closed to allow the disc to centralise itself before retightening the screws. Incorrect axial or radial alignment will result in unwanted air ingress around the discs. Use a thin blade screwdriver to lock the fixing screws by slightly opening their split threads.
Cleanliness of the overall air intake areas and galleries
• With the plenum chamber removed from the inlet manifold clean the whole area of sticky oil and carbon deposits particularly the tunnel and breather/idle speed adjustment galleries. Cellulose thinner is an ideal solvent and pipe cleaners are good for cleaning airways. Replace old work hardened shaft seals with new items to reduce air leaks along the shaft bearings.
• Upon refitting the plenum chamber use a thin smear of instant gasket on the joint and ensure there are no other air leaks anywhere in the intake system otherwise the ECU cannot adjust the petrol/air mixture correctly according to the airflow as measured by the airflow meter.
• It should now be possible to set the idle speed at a consistent 825 - 875 rpm, to remain the same each time the throttle is closed and maintain the CO level at 1.5% +/– 0.5%
Other issues
• Some Single Plenum assemblies were fitted with a throttle stop adjustment screw and on these there was a recommendation that the gap between the disc and the housing should be set variously between 0.002” and 0.005”. It very much depends on how much wear is present and how low the idle speed can be adjusted using the adjustment screw.
• A strange complication occurs on Single Plenum cars fitted with both Hella Cruise Control System and Automatic Transmission. The cruise control quadrant fouls it own support bracket and prevents full throttle opening. Close inspection of this mechanism whilst operating the throttle will reveal this unusual conflict. Removing the bracket and relieving the area fouled by the quadrant with a file or grindstone will cure the fault and allow full open throttle. The acceleration difference is dramatic.
• If, despite all the above there is still an "Idle Speed Hang-up" problem and/or a full throttle impediment, inspect the throttle cable for excess friction, the throttle pedal shaft and its return spring, even a misplaced footwell carpet can cause problems thereabouts.
A common fault on the Rover Single Plenum Efi system throttle mechanism is “Idle Speed Hang-up”. Friction anywhere in the assembly is the killing factor caused variously by damage, misalignment, contamination and maladjustment. Blocked airways and air leaks are also a concern. This action program will resolve the problem.
Ensure that the accelerator cable is correctly adjusted
• Allow some free play but without undue slack. If excessively high idling speed cannot be reduced by turning the idle air adjusting screw clockwise, take the following action.
Check that the throttle plate closes fully
• Warning: Throttle must never be moved by turning the plate/disc, otherwise it will damage the delicate spindle
• The quadrant and its associated linkages are carefully adjusted during manufacture and would not normally be disturbed, except, as most systems were manufactured more than 30 years ago, incorrect fit due to worn parts is now quite common. The following actions can be taken.
• Disconnect the throttle cable from the quadrant and remove the return spring.
• Undo the quadrant securing set-screw/nut/washers and remove the quadrant from its shaft.
• Check the quadrant hub for distortion and undue wear preventing it from securely fitting the shaft.
• Check all the linkages for wear.
• If after the above actions the engine idling speed it still excessive, it may be necessary to remove the plenum chamber to check the following:
Air tight connection between plenum chamber and trumpet housing
• If unable to locate an air leak with the engine running whilst squirting some WD40 along this joint, remove the plenum chamber and check that an incomplete seal between the face of the plenum chamber and the trumpet housing is not allowing air to enter the plenum chamber along that location.
Fit of throttle disc to air intake tunnel of the plenum chamber
• There is not normally a throttle-stop adjustment screw on the original Plenum system and an airtight fit between throttle disc and the intake tunnel is required. Set quadrand mechanism and throttle cable as required to achieve this. However some retro-itted throttle assemblies do have a throttle stop adjustment screw making accurate adjustment somewhat easier. Use a torch to check the gap. A suspect disc can be changed if replacements are available, otherwise clean off all deposits and polish the edges and faces for a significant improvement.
• Use needle pliers to close the split thread of the disc fixing screws before they are removed. Make an identity mark on the disc to ensure it can fe re-fitted the right way around. Inspect edge for dents or distortion and take extreme care with any renovation of the edges.
• Check the spindle for excessive wear or distortion and replace it if required. If new item is unavailable, again, the existing spindle might be significantly improved by cleaning and polishing. The shaft provide primary bearing surfaces so polishing in that area should be minimised. Dress the slot with fine abrasive paper and needle files to remove burrs or dents and ensure that the throttle disc slides smoothly in its slot to aid re-assembly.
• Upon re-assembly, smooth operation without friction in the intake tunnels is paramount. This depends upon axial location of the disc in its slot after the retaining screws are tightened. If the disc interferes with the tunnel, slacken the fixing screws with the throttle closed to allow the disc to centralise itself before retightening the screws. Incorrect axial or radial alignment will result in unwanted air ingress around the discs. Use a thin blade screwdriver to lock the fixing screws by slightly opening their split threads.
Cleanliness of the overall air intake areas and galleries
• With the plenum chamber removed from the inlet manifold clean the whole area of sticky oil and carbon deposits particularly the tunnel and breather/idle speed adjustment galleries. Cellulose thinner is an ideal solvent and pipe cleaners are good for cleaning airways. Replace old work hardened shaft seals with new items to reduce air leaks along the shaft bearings.
• Upon refitting the plenum chamber use a thin smear of instant gasket on the joint and ensure there are no other air leaks anywhere in the intake system otherwise the ECU cannot adjust the petrol/air mixture correctly according to the airflow as measured by the airflow meter.
• It should now be possible to set the idle speed at a consistent 825 - 875 rpm, to remain the same each time the throttle is closed and maintain the CO level at 1.5% +/– 0.5%
Other issues
• Some Single Plenum assemblies were fitted with a throttle stop adjustment screw and on these there was a recommendation that the gap between the disc and the housing should be set variously between 0.002” and 0.005”. It very much depends on how much wear is present and how low the idle speed can be adjusted using the adjustment screw.
• A strange complication occurs on Single Plenum cars fitted with both Hella Cruise Control System and Automatic Transmission. The cruise control quadrant fouls it own support bracket and prevents full throttle opening. Close inspection of this mechanism whilst operating the throttle will reveal this unusual conflict. Removing the bracket and relieving the area fouled by the quadrant with a file or grindstone will cure the fault and allow full open throttle. The acceleration difference is dramatic.
• If, despite all the above there is still an "Idle Speed Hang-up" problem and/or a full throttle impediment, inspect the throttle cable for excess friction, the throttle pedal shaft and its return spring, even a misplaced footwell carpet can cause problems thereabouts.
Edited by honestjohntoo on Monday 25th February 19:00
I had the same problem, tried everything listed but to no avail - it was as if the vacuum advance was being triggered and affecting the tickover. On mine you could also hear the AFM 'whirring' as if air was being dragged in past the flap. After trying everything i took it to a 'TVR specialist' who also failed to identify the problem and charged me £££ for the privilege. Eventally I retarded the timing a little and normal service was immediately resumed.
Haven't been greasing your throttle cable have you? If it's a nylon-lined type then petroleum-based grease will cause the liner to swell and grab the inner cable. Worst case usually found - the hard way - on motorcycles when you try to roll the throttle closed and it won't 
Similar symptoms could be caused by a snapped strand of the inner getting snagged on the outer cable, used to get that on choke cables (I know, you youngsters won't know what a 'choke' is unless it involves a chicken
)
Similar symptoms could be caused by a snapped strand of the inner getting snagged on the outer cable, used to get that on choke cables (I know, you youngsters won't know what a 'choke' is unless it involves a chicken
)Thanks for the great replies chaps.
I have a fair bit to go on with over the weekend.
Don't think its the cable etc as the throttle linkage is closed and up against the idle setting screw.
I noticed that if I blip the throttle the revs come down slow even though the throttle body snaps shut correctly.
Always had a slightly variable tickover but mad now.
Changed the coil and dizzy cap last weekend.
Fault finding weekend me thinks.
I have a fair bit to go on with over the weekend.
Don't think its the cable etc as the throttle linkage is closed and up against the idle setting screw.
I noticed that if I blip the throttle the revs come down slow even though the throttle body snaps shut correctly.
Always had a slightly variable tickover but mad now.
Changed the coil and dizzy cap last weekend.
Fault finding weekend me thinks.
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