Technical Rough idle - choke?

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Technical Rough idle - choke?

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Aug 31, 2013
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Hi all,

We're dealing with a 2001 Punto 1.2 16V.

Frequently, but not every time, the engine seems to run rather rough when idling from a cold start. It will dance around 1k revs running roughly and then settling briefly but then returning to rough. If I drive around for a while and warm the engine it will idle fine. Occasionally you may get the odd misfire when at higher revs driving around.

The head gasket was not long replaced along with a head skim, new HT leads and new sparks. There are no white plumes coming from the exhaust nor any indication of mayo in the oil so I'm fairly happy it's not a head gasket issue.

There are no visible indications of damaged HT leads.

I've just finished a service replacing the oil, oil filter and air filter. I've also cleaned the throttle body as suggested by reading around the forum. The throttle body was very dirty! Could this be an issue caused by the auto-choke? Is it running the mixture too rich? I thought the body being so dirty may be a result of a too rich mixture.

I have MES and the adapters. Could you recommend any tests to help me out? Some numbers to check against the values of my sensors?

Thanks,

Jon
 
Last edited:
Hey Ziggy,

Yes the throttle body was cleaned. The problem still remains however.

A friend suggested that maybe this is being caused by a faulty crank sensor. MES is not reporting an error fault to indicate this but does show some rather erratic spiked to 0 when data is captured over time. Do you think this is a faulty sensor or are we simply seeing a limitation of sampling the sensor so quickly that MES is seeing a phantom 0 now and then?

Captured log:
 
My guess is a bad sensor / wiring.

Mes does not sample I think, it only asks the ecu for samples in memory. And you have to assume that fiat set the sample rate on the ecu correctly.

Anyone care to confirm with a good trace?
 
I too was thinking the data would come straight from the ecu so should be reliable but the fact the desired RPM also has spikes confuses me. Why would that also spike as this is surely a value calculated by the ecu? For that reason it makes me think the spikes are coming form a limitation of either MES of the CAN reading hardware.
 
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