K-Jetronic Idle Surge

[Grady]

I have have a 1986 2.8 V-6 TVR Wedge with the above CIS. Runs fine except:

At a stopped (or slowing to a stop) idle, the revs surge and drop between say 800-300 and 800-0. It will stall out if I don't add throttle. It becomes worse as the engine warms up. Smells way rich too.

I suspect a bad feed-back loop - something to do with the cold start system not turning off once the engine is warm. I have batches of manuals and Internet research but I can't find anything that matches these symptoms.

Any trouble-shooting ideas?

Thanks Grady

[tr7v8]

Long time since I was involved with these but I think some have an idle control valve the other thought is air leak?

[wildoliver]

The first simple check is to see if the rising plate is free and not off centre.

The suggestion it smells very rich would hint to me that it could well be the "5th" injector which will be located around your inlet somewhere, usually a blue plug on it and fuel pipe to it and it attaches with 2 bolts on the flange. Sounds like it may be running all the time, try unplugging it and see if it solves the problem.

[oakdale]

Will most likely just need the fuel/air mixture setting, a thin long allen key goes into the the metering head to do this (can't remember the size).

[Grady]

I worked up my courage and took the the rubber/plastic air cover off (by the fuel regulator) - everything on the air side from the air filter housing to the throttle butter fly valve including the metering plate was massively gunk-ed up. I've cleaned it as best I can, found and fixed a potential tiny air leak and was rewarded - after a couple of hick-ups - with a smooth idle up about 250 RPM to 1200.

However as the engine warmed up, I unplugged and replugged in different combinations the electrical connectors to the cold start injector, thermotine switch and cold start regulator. Nothing had any effect on the idle speed or smoothness.

I'm off to get a K&N air filter cleaning kit and long hex wrenches. Grady

[niva441]

I had this problem. The car ran fine when I was setting the idle speed up, with the bonnet open. However when closed the bonnet squeezed the rubber elbow above the air filter, opening up some cracks. Sealing these up helped, if this is the problem you've got you can see it by push down on it. They appeared at the base of the ribs.

[That Daddy]

oakdale said:

Will most likely just need the fuel/air mixture setting, a thin long allen key goes into the the metering head to do this (can't remember the size).

Rich mixtures on this system(K Jetronic)give surging idles anyway,fix the idle CO 1st before worrying about the stalling,these engines are quite happy to run on about 1 to 1.5 on idle,you may find you have fixed the stalling at the same time here you go https://www.toolshopdirect.co.uk/item.php/store//c... whatever you do don't rev the engine with the tool still in place the throttle plate will move and remove the tool 1st blip the throttle and recheck your CO level.

Edited by That Daddy on Sunday 22 February 21:40

[Grady]

It's a long 3mm T handle. Didn't think about taking it out between revs. Guess I had an extra damper in place. My next Q is where should one start adjusting from?

In my past carburetted cars, there was usually a base point for setting the mixture or idle stop (i.e. screw in all the way in and them back off 2 full turns) before you started fine tuning.

I have a CO meter and started off at 10+. Backed it down to 1.5 with an increase in idle speed to about 1500 RPM. When I went to adjust the idle down, I found it was already screwed all the way down. Backed the idle off about a turn and 1/2 and then reset the mixture. Realized that I had no reference point and quit.

Is there a base point for either the idle or the mixture?

Either way it running much better. Wonder what it will do when cold? Thanks Grady

[That Daddy]

Grady said:

It's a long 3mm T handle. Didn't think about taking it out between revs. Guess I had an extra damper in place. My next Q is where should one start adjusting from?

In my past carburetted cars, there was usually a base point for setting the mixture or idle stop (i.e. screw in all the way in and them back off 2 full turns) before you started fine tuning.

I have a CO meter and started off at 10+. Backed it down to 1.5 with an increase in idle speed to about 1500 RPM. When I went to adjust the idle down, I found it was already screwed all the way down. Backed the idle off about a turn and 1/2 and then reset the mixture. Realized that I had no reference point and quit.

Is there a base point for either the idle or the mixture?

Either way it running much better. Wonder what it will do when cold? Thanks Grady

The throttle idle bypass screw will almost certainly need removing and the housing and screw will need cleaning along with the butterfly(carb cleaner and a toothbrush)then put the screw back in say two three turns from fully in warm up and adjust the idle to approx 8/900 RPM

[Grady]

Answer - Does not idle well at all when cold (and cold in Texas being a very relative thing).

I'll follow the additional cleaning suggestions. Once past the the throttle valve, is the gunk on the intake runner walls OK? And how would one get it off?

[wildoliver]

I always used a bit of petrol on the rubber trunking to pull the crud off, if it is down the inlet tract then scoop as much as you can out with a rag and leave the rest, flushing it through to the head and combustion chambers with carb cleaner or similar will cause more problems than it will solve. To clean the inlet manifold properly it will need to be removed, K-Jet systems are always grubby!

[Grady]

Still dealing with the odd surging idle - Comes and goes. Doesn't matter it the 3 electrical connector (thermotine, other thermo thing and cold stat injector) are attached or not

The two things I haven't tried - rereading this list - is to clean out the idle bypass and re-set the the CO. But I did find a bad (split) air hose coming off the cold start injector.

Haven't used the car too much this spring and I decided to take off the big metering cover and found my gunk is back. Looks like yellow kitchen grease, lighter than it shows in the picture. Clears right off with carb cleaner.



What causes this? Thanks Grady

Edited by Grady on Saturday 16th May 21:46

[Pigeon]

I'd guess you have a crank breather feeding into the inlet tract upstream of the flappy paddle thing.