Revs not dropping back - temporary issue

[Skinne01]

As a long time lurker I've not really had cause to post as I can usually find the info from amongst the wealth of knowledge shared in this forum, however today I have had my first 'event'!

Mid journey to work this morning (about 45 mins in) my S3C decided that it didn't want the revs to drop below 2.5k.
I pulled over and switched off, checked the carpet hadn't got stuck behind the accelerator pedal, checked the throttle linkage was all free etc. All seemed good. I fired it back up and all was back to normal.
Although revs wouldn't drop below 2.5k I did have normal throttle response above that.
I assume this must be some form of electrical gremlin
Any ideas as to what might have caused this?

Thanks
Skinn01

[GreenV8S]

A frayed throttle cable catching in the sleeve would be my first guess. You can test that by checking whether the throttle plate has closed fully when you release the throttle, and whether the throttle opens and closes freely. Alternatively it could be a sticking idle control valve, or an air leak in the brake servo or hose to it, or vacuum lines to the dizzy or fuel pressure regulator. You would test each of those vacuum lines by squashing the hose flat at a convenient point and seeing whether the revs dropped.

[HvdWeerden]

My throttle got stuck in the Swiss alps ;-(( When I opened the bonnet I couldn't see anything wrong. Finally I found out that the throttle linkage mechanism got stuck in the (dropping) bonnet insulation...worth a check !

[jwigglesworth]

HvdWeerden said:

My throttle got stuck in the Swiss alps ;-(( When I opened the bonnet I couldn't see anything wrong. Finally I found out that the throttle linkage mechanism got stuck in the (dropping) bonnet insulation...worth a check !

Snap-the same happened to me but it stuck at 4500 rpm- interesting to say the least!

[magpies]

worth checking the linkage with the engine running and bonnet up - see if it is on the stop or held off. If held off it is likely to be a frayed cable.

[Skinne01]

Thanks for the replies.

It did the same when I drove home (within the first 5 mins). A quick switch off at some traffic lights cured it. I've also checked under the bonnet - no insulation - it's an S4 bonnet if that makes any difference?
I also checked the throttle linkage. It returns to it's stop with no issues and seems smooth in its operation.

I'm leaning towards the ISCV as switching it all off seems to cure the problem. Would that indicate an electronic/electro-mechanical issue? Am I jumping the gun?

Thanks again

[GreenV8S]

On the V8 the ISCV is prone to getting gunked up and sticking - don't know whether the V6 ISCV has the same problem but it seems worth a check.

[TVRees]

OK, it's not for a TVR, but our cars have the Hitachi ISCV, which can be cleaned, so this may be useful .....

http://www.fullsizebronco.com/forum/23-technical-w...

[White S3]

Many years ago I had a similar problem when the revs wouldn't drop below 2500 after a long hack (Portsmouth to Falmouth without the speed cameras/caravans and pleb traffic heading to the West Country for a sunny weekend) it turned out to be the cable termination on the loud peddle jumping out of the recess effectively shortening the cable by 5-10mm - It self rectified shortly after when the cable parted leaving me with nothing connecting peddle to the go faster bit. Temp repair using choc block wire connector until new throttle cable arrived.

(I now currently have an intermittent air leak but unable to find it - frustration! but that is a different story as revs are only 1100 and take time to settle back to 850 after a couple of minutes)

[Skinne01]

Well 'Aubie' went for an MOT and service today.
it passed with 1 advisory for a wheel bearing. It was a knackered ISCV so a new one has been fitted and normal service is resumed.
Also picked up in the service was a leaking brake servo. Fortunately I already had my suspicions and had ordered one.

Thanks again for all the replies.

[Barkychoc]

Did someone say rusty servo?