The V8 Owners Forum -

Hi,

I've not posted on here for years so I've had to re register, but last time this forum was full of useful information!

I'm having trouble with the idle control on the rover V8 which I've fitted to my capri. Its a 4.2L out of a range rover LSE and I using the hotwire system and the standard ECU. I'm not running it with lambda sensors.

There are two main problems that I'm having, idle control and off and part throttle driving and I believe they are linked.

The trouble that I'm having is that when the car fires up the idle is very high before dropping down to something sensible. Then once it has warmed up it either idles far too quickly, around 1500 - 2000 rpm, or it nearly stalls then picks up again, then stalls then picks up again usually to around the same high rpm. You have to give it some pedal for it to clear itself but it just falls back into the same cycle.

The other problem, which I believe is happening for the same reason, is when I'm driving on 0 - 10 % throttle, the engine misses, jolts and is not smooth at all. I think this is because the idle control is cutting in because the engine is running fast than it should be. Basically I can't get any engine braking below 2000 rpm and its never smooth.

I'm not sure how the idle control works on a rover V8 but I'm told there are some electro mechanical valves that open and close to hold the engine speed when the throttle is closed. I don't know where these are or if they are actually working. It seems as if they are opening and closing randomly or they are sticking or something. My thought would just be to bin them and set the idle on the main throttle.

Anyway, does anyone have any ideas of what this could be, and how it can be fixed?

Your help would be greatly appreciated!

It does sound like the idle speed control valve is sticky. I believe it's fairly straightforward to fix. I'm just not sure exactly where it is on the Hotwire system.

Have you searched the forum?, I'm sure there's other posts on exactly that problem.

Chris.

Charlie,

This may be helpful.

http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm

Kevin

Idle control valve is on the back of the plenum with a hose linking it to the throttle valve. Its pretty common for this to get gummed up along with the hose. Well worth taking it off and cleaning it all out, its only two bolts. You might also have an air leak in there somewhere as well so while running get a can of WD40 and spray it round all the joints on the manifold and plenum.

right, I've finally got round to taking the idle control solenoid out. I've doused it in carb cleaner and then put it back in the engine.

I've taken the car up the road and made sure its all warmed up. When I got back home the engine was idling very very very slowly and kept cutting out. I then I gave it a good load of right foot and it started idling at about 1500 rpm again. I tried squashing the pipe that leads from the inlet to the solenoid and predictably the revs dropped.

When I have the valve out the plunger does not move at all - should this be free moving when its disconnected? its go a little bit of play in it but it doesn't slide in and out as I would expect.

any thoughts?



also what is this screw for? is this anything to do with the idle?

It might actually be shot then. I don't think they slide, I thought they were on a leadscrew?

Chris.

Charlie

The idle control valve plunger cannot really be moved by hand. Try spraying it with some carb or intake manifold cleaner. After that evaporates then spray a little pentrating lube(ex: WD40) to loosen it up. Clean the hole in the housing where the plunger fits. Make sure ther is no foreign debris in the housing which will interfere with it closing.

Use a vacuum gage to see if there are any vacuum leaks on the intake. One of the most common vacuum leaks is this: There is a small hose that goes from the fuel pressure regulator to the idle control housing. The vacuum hose that goes to the idle control valve housing not connected is a common cause of vacuum leaks.

90% of all idle problems can be cured by correctly setting the base idle speed of the engine. The base idle speed is set using the screw that your red arrow is pointed to. The correct idle speed is 50rpm less than whatever idle speen your computer maintains when it is fully warmed up.

I can set the base idle on this engine in only 1 minute. Two minutes if I use a the idle speed readout of a timing light for an exact setting. Here is my method to do it:

Only set the base idle on an engine which is thoroughly warmed up. An example would be that you pull into the drive way, get out set the base idle right then. If you set it at any other temp it will be set wrong.

Clamp the idle bypass hose with a pair of vise grip needle nose pliers. Turn the screw(3/16" hex wrench) CCW to increase the base idle speed. When it is 50rpm less then you are done. You can use a timing light digital readout to set it to an exact rpm.

Keep the 3/16 wrench in the car with you for a few days in case you decide to bump rpm up a tiny bit more. At this point you only need this wrench.

The base idle will now keep the engine from ever stalling when your foot is off the gas. The idle control valve will now easily maintain the correct idle.

The computer opens up the idle control valve by 200 steps whenever you turn the engine off(listen to it's buzzing noise when engine turned off). The engine will always idle at ~1500rpm when first started. The rate that it settles down to the correct idle depends on various inputs to the computer at that time.

When ever you do "work on the engine" you may have to reset the base idle.

Randall

Excellent, thanks very much for your help. I think I've found one of the main problems, that being that the vacuum pipe from the fuel regulator is not connected. I'll get on it tomorrow and see if I can make it work.