Heatsoak Help

[NG5]

I'm looking for any help for a problem that seems to be heat soak related with my 1990 SE.

In general terms the car starts, idles and runs absolutely fine. Short runs, long runs no issues other than the occasional small hesitation when flooring it. All temps etc are fine.

The real issue is when I stop when the car is hot (normal running temp), if I restart straight away, no problem. But if I leave it for a few minutes e.g. say filling up and paying for fuel or similar it's very difficult to start, sounds like it's on 2 cylinders and has no power..... and stays that way without improving if I keep driving it (I've limped home that way a couple of times). Leave it to cool for half an hour and everything is absolutely fine again. The problem is getting worse, it only used to happen on very hot days, but now in almost any weather, it happened again today which was hardly hot!

The only code that comes up is 35, idle speed error but most times no error code is generated. All readings on freescan seem normal except idle. It's not actually running on 2 cylinders as I've tried disconnecting each plug both individually and in pairs, 1/4, 2/3, and it makes very little difference and all cylinders are sparking.

With the engine cover open and idling it gradually improves until it is normal again, which makes testing things out difficult!

Something I think is breaking down when very hot but I can't think what, any ideas?

I've changed the IAC and that made no change, I changed the ECU coolant sensor about a year ago and freescan shows it the same temp as the gauge temp, I changed the O2 sensor also about a year ago. Plugs were changed about 2K miles ago. The injectors are still the original, was wondering if it may be that. The coil packs I think are still the originals, but as it seems to be sparking ok I didn't think it would be those.

Any help much appreciated. 

 

[CarBuff]

Are your ignition coils original? Perhaps replacing them will solve the 'heat soak' issue. 

 

Just a W.A.G.

[drdoom]

Were the plugs purchased from a known vendor? Word is that counterfeit plugs have been sold in numbers through various online vendors.

Not a particularly pertinent idea, given the heat soak pattern of behaviour but thought it worth a mention since the plugs are rather new.

 

[NG5]

Thanks guys,

Hadn't thought about the plugs. I think they were genuine, without looking for the invoice they would be from either Opie Oils or the green sparkplug co, both of which are I believe reputable. But it's cheap to change them so worth trying.

I keep suspecting the coil pack but difficult to believe they would both break down at the same time, unless it's the mounting plate. That's £'s to change just on spec. Anyone have a way of testing that without changing it? Same really goes for the injectors, why should all 4 go erratic at the same time.

Any more suggestions welcome or anyone had anything similar? 

[Chillidoggy]

Is it possible to replicate the problem whilst doing a Freescan log? Just wondering if that might show anything up.

[Sparky]

I've seen exactly that behaviour due to a bad injector.  Check resistance values.

[NG5]

Thanks Sparky 👍

As the injectors are the originals, highly likely. Was considering changing them just because of age anyway. I'll do that in the new year. 

[NG5]

Just a follow up. Changed all the injectors for a new set of RS ones, been for a decent drive all nice and smooth, waited 5 to 10 mins. Started and idled fine. So hopefully fixed.

Thanks again Sparky