Help.. Car all over the place after cleaning the VOD

[Admin-bloke]

Thermister is the wrong one then.

EDIT: The thermistor sounds like it's the right one

If you're desperate for banjo bolts or washers I'll post you some.

Sounds like you're getting there

[flux3d]

lol, very true Rob, and now i can strip the engine down to the VOD and put it back again in record time!

[flux3d]

thanks Nick, Ordered twelve online. They came to about 15 quid, but the next day postage was the same again! Expensive bolts. Hope they are the right ones. 8mmX1 ptch, short versions

Yeah, sensor seems out. At least its reading lower resistance overall than stock, which means a fast idle situation shouldn't happen right? The ECU only causes a high idle if its ABOVE 12K? Can I just jumper the connection at the ECU with a 12K resister? The car never goes out in the winter anyway.

[Admin-bloke]

Yes, you can replace the thermistor with a 12k ohm resistor. Or put a10k ohm resistor in series with it.

[flux3d]

Well, Banjo bolts in but the car still idles at nearly 2000rpm! Here is what I know:

Dwell adjusted to swing between 40-50 at 90 degrees, 4 cylinder etc.
O2 plug unplugged it defaults to 45
Full throttle it jumps to about 53, so all good there.
Vac pipes all correct and not leaking
Fuel pressure seems good
Can't check CO2 as I don't have the equipment.
Pipe of agony is in correctly
Idle motor seems ok, although unplugging it has no effect of the idle speed
When warm there seems to be no vac at the back of the distributor, which from what I can see is correct for spark advance
The thermister is showing an incorrect value. About 3-4K with a warm engine. Jumping this connection seems to have no effect on the idle.

I'm stumped.

[Horsebox]

I'm new to these cars and have no real mechanical experience, but I've managed to fix my idlespeed system so I may be of use...

Can you pinch closed one of the air pipes to or from the idle motor, to see if the rpm drops? My thinking is that assuming the idlespeed system works, it will have already closed the valve to try to reduce the idle to spec. If you pinch a pipe and nothing happens then it's fair to say the motor is closed. If you get a reduction in rpm then your idlespeed system isn't working.

It's a crude test I know, possibly damaging to a brittle pipe, but I've read this all the way through and really feel for you with this problem.

If you do the test and can say your idlespeed system is u/s, as mine was, one of the Volvo manuals deals with troubleshooting the system. It was so straightforward that I could do it!

Let me know if you can't find this manual and I'll email it to you.

Sounds like you're nearly there!

Your patience with repeatedly rebuilding the induction is biblical...

Mark

[Horsebox]

Your thermistor looks bang on spec to me. Mine shows 3.3k Ohms after a five min warm up.

Ref: page 93 of the Volvo Service Manual for CI fuel systems B27, B28E/F

Ungrateful bastard eh (the car!)....you just wanted to help it!

Edited to clarify who the ungrateful bastard was!

Mark

[Admin-bloke]

Make sure that when the throttle is closed that the micro switch is engaged. If not, then the ecu will open the idle speed control valve to the fully open position and will cause the engine to idle high.

If there is a fault with the idle system, you can temporarily replace the Idle speed control valve with an isolation valve from a plumbing store/ b and q and open it enough to let enough air in to regulate the idle speed.

Alternatively, remove the idle speed control valve, block both pipes with bolts/ wine corks and adjust the throttle plate open to set a fixed idle speed.

You could have a problem with the ecu in which one of the output transistors is not switching causing it to seeing fully open, but double check the switch and its wiring first.

If you can drive the car in this

[Horsebox]

Admin blokes first paragraph of previous post is a much better idea. Try this first before potentially damaging pipes by squashing them.

If it's just a case of the idlespeed switch not being triggered then you're laughing...

Run the engine and poke the switch with a long screw driver to see if the idle system takes over and drops the rpm.

Tonight's the night....

[Admin-bloke]

I was going to say "If you can drive the car in the current state and can get it to my place I'll have a look". (I have spares on the shelf courtesy of Jay)