Technical Sons '98 Punto S - Idling/other problem

[johnlumley]

Hi Guys,

New to Fiats, just bought the lad his first car and having a bit of a problem..I'll list the facts and hope you can come up with helpfull ideas...

1. Bought car 3 weeks ago, ran AND idled perfectly. 70K miles, 1242cc 8V.
2. A week ago, head gasket went, lots of fuel/water/antifreeze went through the engine/exhaust. Got a mate (mechanic) to help.
3. Changed head gasket, cambelt, tensioner, rocker cover seal, engine oil, filter, plugs, HT leads, air filter, skimmed head before re-fit, all decent kit, no cheap stuff - Bosch etc.
4. Engine and all looked good internally, like it had been well maintained etc.
5. Engine now idles roughly/imbalanced, but car drives nicely (maybe underpowered?. Starts fine too, but dips too low & comes back to an imbalanced idle again.
6. Took it for a good thrash on the motorway to get it hot, settle it & clear it out, but no difference.

This engine ran and idled perfectly, now there's defo something not right.

I've read about Lambda sensors causing idle problems - could the water/steam have damaged it?

I've read about the CAT being damaged with the "trauma" ... is that possibly the problem.

Last detail, when I high-rev the car stationary it revs high, then drops (a bit) then rises again, and repeats, with regularity as if it is being switched up and down.

Please help if you can, I'm out of knowledge and dont want to keep changing parts unnecessarily.

Many thanks

John

 

[reddy4bed]

Sounds like the classic timing belt fitted incorrectly. Use the hole in bell housing to accurately set crankshaft tdc rather than the line on pulley.

 

[D4nny8oy]

Lambda faults usually cause a 'surging' when driving on a steady throttle opening.

If it's taking a while to return to idle when revved at a standstill, it indicates a possible air leak on the inlet side, or an idle stepper motor that's sticking/lost it's position.

It may need the self-adaptive settings reset at a dealer, though try this first- Switch on the ignition and leave for approx 1 min, switch off and wait another minute. Now start it and allow it to warm-up until the fan cuts-in. This is a basic manual way of resetting the stepper motor and can cure simple issues.

Otherwise check for leaks by getting a can of WD-40 or brake/carb cleaner and spray around the inlet manifold/throttle body joints and see if the idle speed increases.

 

[johnlumley]

RESULT - REDDY4BED

Right first time !!!

Cambelt check using the bellhousing marks - one tooth wrong.

Much appreciated for the replies, it's idling and running smoothly again.

Thanks

John