Hi all, I recently changed the coolant temp sensor on my 1999 1.3 mpi felicia. Did this in hope of curing the almost stall that i sometimes got. What it did was to boil my engine after only 3 1/2 miles! Have put the old one back, can put up with the bogging down once or twice a day. So now I have a car which starts first time veery time, bogs down at low revs once in a while and now, weirdly, is sometimes very slow to come back down to idle if I rev it. Saunters back down from 2000 revs as and when it feels like it, settles down at marginally under 1,000.

Don't know where to go from here, except maybe a garage with skoda diagnostics. Can anyone hazard a guess at possible causes / cures? Thanks again,

Martyn (West Yorks)

Sounds weird...

I can't understand how a replaced temp sensor can cause overheating? Unless it's the wrong type of sensor and therefore somehow interfers with the coolant flow (not very likely)? I thought the sensor just sent information to the ECU and in no way affected the coolant system?

A faulty radiator fan sensor can of course lead to overheating, but that's a completely different matter.

What abour your thermostat and stat housing? Are they in good shape/changed recently?

Well, the sensor was bought from Jorily. i called and spoke on the phone about the different colour band ( the new one is yellow, the old one is blue), and was assured its all the same one now. The physical shape of the "wet" end is completely different, but I dont think it should interfere with the stat working as it doesn't seem to project any further into the housing. With the engine running, the coolant is pumping round merrily and going into the expansion tank, so it looks like the stat was operating. Housing seems to be ok. Much head scratching!

Head scratching indeed. I've understood that Jorily is a reliable supplier of parts, so the sensor is probably the correct one.

I've no other suggestions than the old and tedious ones: change stat and housing (even if they might be OK now they will break sooner or later), give the coolant system a good flush, check the radiator fan sensor so that you know that the fan cuts in when it should, re-fit the new temp sensor and see what happens.

But others might have better suggestions.

I wonder if bleeding the coolant system could have helped? Running the engine with the coolant cap off till it gets up to temp and massaging the hoses can encourage air out of the system.

As for the nearly stalling issue I would try cleaning the throttle body butterfly valve with carb cleaner. It should be visible with the air filter box top removed, and closes and opens with the accelerator pedal.

if it's boiling, either you have an air lock or the stat isn't working..

the bogging down problem sounds like a throttle body related issue

the silver end of the sensor as apposed to the black end is the new type. The sensor with the yellow band is certainly the right one.

I note you say that putting in the new sensor boiled your engine. Does that mean that the water actually boiled and came out somewhere, or just that the gauge went right up? When I changed the sensor in my 1.9 diesel (temporarily), the gauge immediately read about 20% higher than normal, but that was just a false reading.

I agree with a previous post about Jorily - they seem pretty knowledgeable and trustworthy to me. Odd though it may seem, I would also suspect that the issue lies elsewhere than the sensor.

Good luck and best wishes,

Mr Music

Regarding parts and advice from Jorily. I would like to say right now that there has been NO problem with parts, advice or service from Jorily. I was stating the source of the parts to indicate their reliability, I seem to have been misunderstood and assumed to be questioning the quality of parts or advice from there. Nothing could be further from the truth, in fact I have had an email (10.23 on a Sunday morning!) giving more helpful advice from Graham at Jorily. Hope that's cleared that up!

Right, thanks to all for advice and help, I've cleaned my throttle body this morning, there's a small amount of wear in the shiny areas swept by the butterfly but it looks and feels ok. Reconnected ecu and battery after 3 hours off, turned ignition on and waited a couple of minutes, fired it up. Idles at 1,000 rpm. Tapped the gas, shoots up to 2,000rpm and stays there till i tap the gas again! I need this car at 5.30 tomorrow morning! Any ideas?

try opening up the plastic housing on the side of the throttle body and spraying some switch cleaner on the throttle pot wiper track

Plastic housing? Mine looks like a metal one with loads of little bendy lugs clipping it on. Got any pics? EDIT>Right, so mines the simos. took the cover off, cleaned the graphite tracks, ticks over at 3,000rpm now! Disconnected batt/ecu again, will try seeing if it resets. Desperate now, no busses for postmen at 5.30 tomorrow:worried:

Edited 21 September, 200817 yr by turbocroat

shameless bump:)

If your car is really undriveable in it current situation and you desparately need it, heres one possible idea.

Disconnect the carb / throttle stepper plug and drive the car without it. Had a problem with our felicia throttle several years ago, probaly needed resetting but we just disconnected it and the car still made it through 4 consecutive MOTs. Absolutely no effect on MPG, only noticeable change was that tickover went from up about 150 - 200 rpm from stock 750ish rpm.

Even though your car ticks over fast does your car not calm down once its in gear and rolling under load?

so the car is revving on its own accord?

the only car I had that done that was my Astra but that only seemed to happen after the car was warmed up in town traffic.

you'd only need to change the stat if it overheats.

I can't offer any other useful suggestions as despite driving a Felly for 2 years and knowing bits I'm still a n00b.

you might have a vacuum leak somewhere

Or poss a dirty or slow switching oxygen sensor (or llambda sensor) not sure on Skoda terminology. Has been a problem on older Fords. but as has been said i would check for vac leaks first. On the sensor i would suspect that you had an air lock. this would make the sender unit warm up in air not water very quickly, and also your ecu would get a false reading and would start to weaken the mixture as the temp falsley(?) went up coupled with your idle fault the revs would increase.

Like i said the terminology is different but the operating principles would be the same.

Firstly, thanks to all who replied, much appreciated guys. Secondly, it's still at it! Took it to my local garage, he plugged it in to his laptop and said "throttle body wants cleaning." Did that, reset it all, no better. He said 99.99% sure to be a failing throttle body. Looked for recon/ refurb, eventually coughed up for a brand new one from Skoda. Ulp! Empty pockets now, garage fitted it and said it was ok. Took it home and it got worse and worse. Symptoms now are: Occasional near-stalling, whether hot or cold. Revving at 2000 rpm and not settling down. 1.3 mpi 199 fellicia, new throttle body, new temp sensor, now the speedo has started to fail. Mechanic says sensor in diff possibly faulty, but I thought it was cable drive speedo? Mechanic says maybe ecu now, wish he'd make his mind up! Go on, guys, give it your best shot! Otherwise I will shortly be selling one brand new throttle body with a car attached!

If the ECU was faulty I am pretty sure the car would not be working at all, as the two flavours are working or dead - so I would rule that out.

As you say the speedo is cable driven - so the points for that to fail are the speedo head itself, the cable, or the drive gear. If it's "starting" to fail it's probably either the cable is routed near the inlet and getting hot, or kinked - so that's worth checking.

Don't know if you've checked for a vacuum leak as suggested above yet? Someone on here posted the trick of spraying carb cleaner around the inlet manifold gasket to check for leaks - if there's a leak the revs will change. I'd give that a go before going to another garage as it will only be a fiver for a can of carb cleaner.

Please, please, please as anewman suggests check for a leak at the inlet manifold gaskets and to be honest change them anyway they are only a few quid. These are classic symptoms of that.

I am willing to bet that this will cure it as i had exactly the same problem. The problem with diagnostic computers is that that is all they are, always check the basics and least expensive option. My advice would be to change gaskets and if this fixes it which i suspect it will put your old throttle body on and see if it is ok.

If all is well stick the new one back in the box and send it back!!!