[lsowden12]

Head gasket was replaced 11 months ago following a 6 month long hellish search for whatever was causing my severe idle problem, it was the gasket.
The cooling fan has been running constantly since well before the gasket was changed. Fast forward to today, until last week the car was almost impossible to start when cold (20 seconds on the starter before it runs). Identified that the CTS was completely broken, gave zero signal. I have replaced the coolant temp sensor, the car now starts straight away but the fan is still running constantly.

The idle is stable and doesnt hunt but it will never idle at the normal 900rpm. It sometimes idles at 1000 rpm, you can drive 100 feet and then suddenly its idling at 1250rpm, drive 10 feet and hold the clutch in and its idling at 1500rpm, its completely impossible to work out whats going on. The brake does hiss and the idle does increase if you pump it a lot, suspected air leak in the brake servo BUT if I disconnect the vacuum line and tape up the hole on the manifold and drive around for a bit the idle issue is just as bad. It does burn a decent amount of oil, the car smells of coolant from the exhaust but I've monitored the level for the past 2 months and it hasnt even dropped 1mm so I dont understand why I can smell it. The car also feels underpowered compared to 3 years ago before everything started going wrong. I own a 1.6k coupe which only has an extra 5 horsepower and that feels like a rocket in comparison.

All in all I have replaced the fuel pump, fuel filter, HT leads, distributor cap and rotor arm, coolant temp sensor, catalytic converter and backbox, cleaned out the ECU vacuum pipe, throttle position sensor, oil and oil filter

I am genuinely completely lost on what to do, I'm just hoping to god someone has found something completely random I could have missed that would cause all this. I REALLY dont want the gasket to be gone again

[g259fsg]

Sounds like you tried and eliminated quite a few things. My 214 is an earlier model than yours, but on mine, if the fan runs continuously then the thermostatic fan switch on the radiator is probably faulty. It should be open when the car is cold.

If you are still suspicious about the head gasket, you could do a compression test and also monitor the coolant header tank for exhaust gases using an exhaust emissions analyser to sniff it.

Have you got a diagnostic tester, e.g. RoverMEMS App? This might tell you what parameter is changing when the idle sits high. Could be the Throttle Position Sensor is faulty. I think on later cars, the ECU reads the TPS to determine if the throttle is in the idle position. There is a routine for setting this up with the ECU. My early 214 uses a throttle switch to check for idle position on the accelerator.

Good luck,
Hugh

[nickg90]

check all the vacuum hoses to fit well and tight.not only from the oil trap to the ecu but also behing from the inlet manifold.use the diagnostic cable as the g259fsg told you.you will have a clear image to idetify whats goes wrong.where you find the tps?

[lsowden12]

Yep, done a sniff test now, no head gasket leak. The tps has been replaced and I’ve driven it around for 50 miles with the brake servo vacuum line disconnected to eliminate the servo leak from the suspects list even if it’s still a problem, idle was still just as unstable and the cooling fan was still on.

I was unaware the radiator itself has a fan switch, I’m starting to think the idle is related to the electrics when the fan is running because the ecu is seeing unstable voltage and is kicking the car into a limp mode of some sort. I’ll have to have a look but I’m still completely stuck on this. I think what I may do now, whilst it’s 0 degrees outside for a few days, is disconnect the fan completely and drive around without the fan to see if it stabilises

[itcaptainslow]

Has a compression test been performed to rule out a mechanical/timing issue?

Even better if a cylinder leakdown test can be done, too.

[Mr Teddy Bear]

If the fan runs from cold that is a short circuit across the fan switch [thermistor] in the side of the rad.
You can prove this by pulling off the plug and bridging the female sockets with a piece of wire= fan runs.

I'm assuming it's the other one that you've changed?

[g259fsg]

That's a good point. The fan switch is completely independent of the ECU or temperature gauge, so if you pull the plug on it then the fan should not run at any time. It is just a simple thermostatic switch, not a thermistor. There are two coolant temperature sensors (certainly on my early K-series) both using thermistors. One measures the coolant temperature for the ECU. If this is faulty or intermittent it could give faulty temperature readings to the ECU and it sets the wrong idle speed and fuel injection. This is usually diagnosed with the ECU diagnostic tester. If at any time it shows 60 degC, then the ECU is using a default value as the coolant thermistor is out of range. The other coolant sensor is for the dashboard temperature gauge. Even if this is showing the correct temperature, the ECU may be getting a different message.

[g259fsg]

One thing you mentioned that the issue might be affected by battery voltage. The ECU monitors battery voltage and if it is low, it increases the engine RPM, but not as high as 1500 RPM I think. Is the battery and alternator working fine? At idle you should be getting around 14V without lights etc. switched on. The radiator fan does draw a few amps of current.

[lsowden12]

Yeah so I ran the car without the fan plugged in at all for about an hour, idle dead stable at around 1100, doesn’t fluctuate, doesn’t change based on distance driven so it’s definitely the fan affecting the idle pretty badly. I had no idea the fan was independent of the ECU, if I can get the switch changed that’s the next thing on the list. Appreciate it guys