new engine is in and it starts fine, but I have a high/racing idle and it hunts for a few seconds after you blip the throttle then races again.

I should say that it did this before the engine change as well.

I've tried

Cleaned TB & reseated gaskets
Swapped injector (from a scrappy)
Swapped ICV (from a scrappy)

Any ideas?

Probably just replace the throttlebody

paul12345 said:

Probably just replace the throttlebody

Click to expand...

Can I ask your reasoning?

Does the problem go away once the engine is warm? If so then yes dirty throttle body. If its the same even when the engine is warm it's something else.
Check the timing is okay

Throttle body and inlet manifold were spotless when I put it back together. Drove the car for 10-15 minutes and it was still there, although the temperature sensor is kaput I think as it was showing no temp at all even after a trip on the dual carriageway.

There are a few TBs on ebay with all the sensors included maybe I'll just do that

Throttle body is fine if it's at all temps

I had a silmilar problem, most of the sensors can be unhooked and the ecu runs on default figures, so disconnecting the lamba sensors water temp senor etc made no difference.

Hooking up a kkl interface with fiatecuscan showed bit of a abnormal reading on the throttle position, I got a replacement TB for £20 and all sorted.

paul12345 said:

Hooking up a kkl interface with fiatecuscan showed bit of a abnormal reading on the throttle position, I got a replacement TB for £20 and all sorted.

Click to expand...

Intriguing. What was the abnormality? The last time I connected to the ECU it showed ~9 degrees open even at closed throttle - Is this similar to what you were experiencing?

Played around a bit more.

Can't hear any hissing through a tube when putting it around the TB (although to be fair, my hearing isn't too good with loads of background noise).

Removed vacuum line for brake servo and blocked manifold hole, no difference.

Removed MAP sensor line and blocked the manifold hole; engine idle went to 1k but ran like crap. Leaving the vacuum line connected to the MAP and simply unplugging the connector did the same thing.

If I block the small vacuum hose going to the air box, the idle seems to be fine.

I reckon there HAS to be a vacuum leak somewhere but I have no idea where it is coming from.

Hi again,

Thanks everyone for your replies.

I inspected the TB more closely and it appears the fuel pressure regulator (I think that's the thing in front of the injector screwed into the TB with 4 torx screws?) has been tampered with.

I suspect the previous owner screwed around with the TB to get the car to idle correctly, since the head gasket was knackered when I got it but it still idled at 850 rpm.

Since I have no idea what he has or hasn't messed with I decided to buy a whole TB and inlet manifold with all sensors for £31 delivered. I spoke the guy and he is confident it all works.

If it's not that then it can only be the MAP sensor or something to do with the EVAP canister thingy...

ST60SX said:

The temperature sensor is kaput I think as it was showing no temp at all even after a trip on the dual carriageway.

Click to expand...

Has this been rectified as the ecu will think it's a cold
engine putting in more fuel choking the engine (hunting)
and increased revs. Could be sensor or damaged wiring.

John

Does the mk1 have two temperature sensors? I read something about it in this thread, although this is a punto 75.

One for intake air temp (in the manifold; goes to ECU) and one for the coolant temp gauge (in the head, near the dipstick)?

The one in the head came with the new engine, it may well be faulty. Last time I checked ECU the temp was fine so the one in the manifold should be OK. I will double check tonight.

Temperature sensors tend to be pretty tough (resistance bulbs). Lambda O2 sensors (although they run in hot exhaust gas) are easily damaged. If the O2 sensor is not changing its signal value enough the engine will run as if its on choke. his can make it stumble on tickover.

On all those vac pipes make sure non are split. They tend to go with a longitudinal split that can be hard to see.

I changed the temp sensor in the head and the gauge works again now at least. Cooling fan kicks when the temp is at midway. Coincidently, I think the temp sensor fitted was the wrong one as it was a ~23mm socket (other one is 19mm) and was a lot shorter.

When the engine was warm (when the fan kicks in) I disconnected the lambda and it didn't really make any difference to the idle speed, or the engine tone in general - could it be faulty?

Another thing was that if I force the throttle closed (it doesn't move a lot obviously), the rpms decrease very slightly... the cable isn't tight or anything though. I have a new TB turning up in the next few days, that should rule a few things out. I can have a good look at all the hoses then as well.

New TB arrived today, pretty fast!

Anyway I fitted it and.....................................






It works, hurrah! Problem solved! RPM was about 1200 when it burst into life, settled at 1k within a few seconds then died down to ~850 after about 20 seconds. Thank goodness.

I didn't use the manifold I got with it (the bolts are a PITA to do when engine is in the car) so just swapped the TB and coolant sensor over.

Unfortunately I can't be more specific about what caused the problem as all the associated sensors, injector, fuel regulator, butterfly etc are all different now.

I took it out for a drive and there might be a bit of a flat spot around 2.5k rpm (although it could be my imagination); the new TB is a bit dirty and I have some new HT leads so hopefully that solves that, I'll also shove some redex in at the next fill up.

Thanks for all your help guys, my Punto is finally working again!!!!