K series idle problem

[rkanaga]

I would be very grateful for some help on this.

 

My 1996 1.4K series Supersport is having some 'issues'

Initially it was cutting out on idle when hot. The problem could be fixed by doing a TPS reset and so I have replaced the TPS and this seems to have helped. It no longer cuts out when hot. It was then cutting out occasionally on a cold start but nothing like as bad so I lived with that. I also took off the throttle body and cleaned the hunk that had built up behind the butterfly valve as I understood that this can also cause idle issues (the car had a K&N oiled air filter and so this is a common problem with this setup I believe.)

 

I got the car out for a run yesterday and had a different problem. Once the car had warmed up, the idle seemed to gradually increase, eventually reaching around 4K by which time the car was pretty much driving itself! The only solution was to turn th engine off and on again which fixed the problem but only for a few minutes. A TPS reset also helped but again only for a few minutes.

 

I've checked for any air leaks and everything seems to be connected, the air filter was a tiny bit loose so i have tightened this (being careful not to overdo it and distort the throttle body.) The stepper motor can be heard chattering when you do a TPS reset, however the pin does not rise up when doing a reset. Should it do so? I took the stepper motor housing off and the stepper motor steps both ways when you trigger a TPS reset  with the housing off yet the pin does not seem to rise from the lowest setting when it is reassembled. The pin itself seems to move freely and is nicely oiled.

 

Is it possible that the stepper motor is too weak because of some wear issue inside the motor?

 

I presume that there isn't an IACV in these cars because everything is done via the stepper motor adjusting the throttle directly? (I know that a dirty IACV is a common cause of idle problems.)

 

Is there anything else I shoudl try?

 

The dealer has been great and I'm sure would happily look at it, but they're a bit of a drive away, and  part of the fun of these cars is trying to understand the problems yourself so I wanted to at least do the basics myself first!

 

Many thanks

 

Robin

 

(also does anyone have a fix for the speedo needle flapping around madly, the rev counter is nice and smooth but the speedo seems very loose.)

 

 

[SM25T]

Do you have a plastic inlet where the air filter attaches .... if so, check the clamp band is not too tight. Can cause the butterfly to stick.

[Jonathan Kay]

... also does anyone have a fix for the speedo needle flapping around madly, the rev counter is nice and smooth but the speedo seems very loose.

Original mechanical drive from the gearbox?

Jonathan

[John Vine]

...a fix for the speedo needle flapping around madly...

For a 1996 car, I imagine your speedo is cable-driven from the gearbox via an angle drive.  Your symptoms sound like a damaged quill (connecting the gearbox to the angle drive).  If the quill is ok, remove the cable inner and check for damage.

JV 

[rkanaga]

Thanks John, I'll pull it out and have a look. What would damage look like by the way? It has been suggested that the guage might need repairing, but the quill or cable would be a lot cheaper! The guage is working, just that the needle flaps around a lot.

[John Vine]

Look for damaged wire threads, such that the quill/cable no longer rotates at an even rate.

 

JV

[Jonathan Kay]

Robin: Do you already have the fitting notes from the Assembly Guide?

John: Do you know of an exploded diagram etc of the mechanical drive with the right-angled adaptor, please? Anything better than the one below?

It has been suggested that the guage might need repairing, but the quill or cable would be a lot cheaper!

Could be any of them, but it's a speedometer so I'd follow John Vine's advice. :-)

Jonathan

[CageyH]

Thanks John, I'll pull it out and have a look. What would damage look like by the way? It has been suggested that the guage might need repairing, but the quill or cable would be a lot cheaper! The guage is working, just that the needle flaps around a lot.

My needle was flapping around. It was the 90 degree speedo drive that was worn on my car.

[John Vine]

Re #7:

No luck I'm afraid, Jonathan.  All I have are the photos from a Haynes Sierra manual.

JV

[EEK]

Try driving the cable with an electric drill when disconnected from the right angle drive, if OK then try with the right angle added to cable etc.

[rkanaga]

We managed to get to the bottom of my K series idle problem:-

The car is a 1997 1.4 K series supersport which I bought from Damian and Anthony at GP Sevens. I built an almost identical car whilst in med school and always regretted selling it so it was great to find an almost identical 6 speed to drive again, differing only in having cycle wings, which I actually now prefer.

 

The car developed a curious problem, initially stalling at idle when hot. After a replacement TPS which Damian kindly sent me to avoid a trip back to Sevenoaks, and cleaning the oily residue from the throttle body (from the oiled K&N filter) the symptoms changed to now stalling at idle when cold, and then as the engine warmed up the idle speed would rise and rise to as much as 3K. Doing a manual TPS reset helped but only for a few minutes, and I was curious because whilst you could hear the stepper motor chattering when you did the TPS reset, it did not appear to move at all.

I dropped the car back to them, and Chris there very cleverly worked out the problem, dry solder joints on the feed to the stepper motor (the board is inside the motor housing). A quick resolder and it is now working perfectly. The car has done 33,000 miles so presumably just the result of vibration over the years as I  think 1997 was before the use of lead free solder?

I've seen a few other threads about K series idle problems and I do wonder if any of them actually had this fault. Because the fault is intermittent it results in very inconsistent symptoms and so you might actually find that fiddling with other parts of the system might work temporarily only to induce other issues later. The clue in my case was that stalling at idle and then running fast when hot implies running both too lean and too rich which points to a sensor or actuator fault I suppose. You might even think the ECU was faulty I imagine.

 

Anyway, thanks to GP Sevens who have been fantastic in sorting this out and are great guys to buy from, and of course for getting me back in a 7 again!

All I need to do now is stop planning upgrades and just drive it! (iIve even bought some noise-cancelling headphones for long trips..)

 

Robin

 

 

BMW 650i

Honda NSX (1991 manual)

Caterham 7 1.4 K series Supersport 6 speed