Pinto 2.0 EFi rough idle when cold

[peter_m7uk]

Hi All,

My Pinto 2.0 EFi idled absolutely fine when cold, until recently.  I used to start it and it would automatically rev at about 1200-1500 rpm until it warmed up a bit, then drop to 800rpm, nice and stable.  These days, I start it and it almost stalls, then the revs pick up for a few seconds, before it almost stalls again, then it finally settles into an 800rpm idle.

Once it's hot the idle is fine, so what's going on specifically when cold?  And where has my initial high idle speed disappeared to??  

Thanks,

Pete

[IanS]

Idle Air Control valve is sticking.

It is an electricaly controled valve that gives bypass air round the throttle body. (efectivly it changes the throttle stop by allowing more air post the butterfly valve, the ECU takes care of the petrol)

It is held on by 2 screws and has a single electrical connector.

Remove the 2 screws and spray carb cleaner into the body, refit and if I am correct the idle will be back.

Too much carb cleaner is better than not enough, 20 second squirt should do.

[peter_m7uk]

4 minutes ago, IanS said:

Idle Air Control valve is sticking.

It is an electricaly controled valve that gives bypass air round the throttle body. (efectivly it changes the throttle stop by allowing more air post the butterfly valve, the ECU takes care of the petrol)

It is held on by 2 screws and has a single electrical connector.

Remove the 2 screws and spray carb cleaner into the body, refit and if I am correct the idle will be back.

Too much carb cleaner is better than not enough, 20 second squirt should do.

Hi Ian, thanks for the suggestion.  It's one thing I'd considered, but doesn't that valve work when the engine is hot as well?  My thinking was that, if it was the idle valve, it would always idle badly, not just when cold..   As it's pretty easy, I will have a look anyway.

Cheers

[IanS]

https://www.ebay.co.uk/itm/163058114655?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338767030&toolid=10029&customid=eb%3Ag%3Avms%3Aeb%3Ap%3A163058114655%3BEAIaIQobChMI5M7Z2-Le8gIVErrtCh23pgkVEAQYAiABEgLYS_D_BwE&_trkparms=ispr%3D1&amdata=enc%3A1TVc_0P-_SCyOoDTfyi-j3g48&gclid=EAIaIQobChMI5M7Z2-Le8gIVErrtCh23pgkVEAQYAiABEgLYS_D_BwE

Gives you an idea of what to look for, they are robust but do need cleaning every so often, a new one should be a very last resort.

[IanS]

There is a throttle stop screw on the throttle body that is preset for hot idle. Do not adjust without a very very good reason.

[IanS]

I should add that ECU controls hot idle by retarding ignition timing, adjusting the throttle body stop can confuse the ECU.

[Derek]

I found this article very useful when I had a Pinto running EFI. Ian's suggestion solved the cold idle problem I had too.

 

 

 

[Jez Morton]

If its OK warm, I'd be looking at the temp sensor in the manifold. Mine went but other way around I would get high resistance when hot so would rev at 1200 when hot. Sounds like you may have a short or low resistance when cold.

[peter_m7uk]

Thanks, but the idle valve certainly doesn't seem to be stuck, I'm inclined to look elsewhere before I consider a new one.  I will try measuring the voltages given on page 3 of Derek's article...

Edited September 19, 2021 by peter_m7uk

[peter_m7uk]

Update - I measured the coolant sensor voltage..  When cold, it was 4.4v.  Just after I started the engine, it actually rose above 5v.  Then when hot, it dropped to around 3.4v.

This is obviously pretty different to the 3.5v cold and 0.5-0.8v hot in the article above!  So I suspect that's the culprit, the voltages are way out of range. Now where do I buy a replacement??  Mine needs a spade connector, but a quick online search so far shows sensors with round connectors...  

[Jez Morton]

Are you sure your looking at the right sensor? There's one in the cylinder head near the dizzy with a spade connection and one in the middle of the inlet manifold with the round connector. Cylinder head sensor is for temp gauge and manifold sensor is for efi.

[Grim]

I checked my sensors recently after an unrelated fault in the injection manifold loom. I got ~4.4v cold and it turned out it was completely disconnected. You ought to rule out a wiring fault before replacing the sensor. Disconnect the multi plug on the sensor (on the inlet manifold between cyl 2 & 3) and measure the continuity/resistance of the wires to the ecu.

Edited October 11, 2021 by Grim

[peter_m7uk]

I measured the voltages, but they seemed to be about the right ballpark, so I left it for a while...   Now the engine won't idle at all, never mind when it's cold!   So probably not temperature-related and I've ended up ordering a brand new idle control valve for £35.  I opted not to clean, as I cleaned the existing valve before and it's plumbed in without a connection to the cam cover, fresh air intake only.  It's a 33 year old valve that had already done 100,000+ miles, so let's try a new one!  Fingers crossed that does the job, anyway  

[Grim]

Where did you get the valve from?

[peter_m7uk]

On 5/30/2022 at 11:51 AM, Grim said:

Where did you get the valve from?

I got it through Amazon