1990 740 b230f, erratic idle when fully warmed up- 10/15 mins of operation. removed head to have plug theads chased, checked head for warpage - found none, reinstalled, replaced head & intake mnifold gaskets & idles erratically. did not do this before removed head. since have replaced plugs, plug wires, distributor cap & rotor, coil, o2 sensor, temp sensor, air mass meter, idle air control valve, fuel filter, fuel pump check valve, air filter, checked all line & hoses for condition & leaks, fuel pump regulator, listened to injector with stethescope for clicking, injectors each have 16.0 ohms, all fault codes now cleared, 1-1-1. any ideas?

OK, I've read all the other posts and the first thought I have is maybe your valve adjustment is too tight? Did you recheck the clearances after the head and cam was all installed and torqued down?

My thinking is that when cold maybe the clearances are OK but when warmed up theY are ????????

Man, you must have spent a bundle throwing parts at the problem. Did you have the valves checked for guide clearance and freshened while you had the head off?

If the symptom only appears after the engine has warmed up, I'd suspect a vacuum leak that appears after something metal or aluminum has expanded from the heat.

Please please, stop replacing those expensive parts and diagnose the problem.

What do you mean by erratic idle. what is the idle speed with AC on and AC off? Does idle speed move up and down, is the engine missing at idle. Any other performance problems?

Have you changed the seals on the injectors themselves?

Put a meter on the fuel pressure regulator to see what it is doing?

Regards

Peter,

I am suffering from the same problem as you are for the past 2 years. But my engine is B234F. Yeh.. 16 valves. But the idling in my machine is not erractic. If the A/C is On, no problem with the idling. It idles around 850 to 900 rpm. My car is an auto trans. But the very minute the A/C is turned off, I can see the rpm needle would be waving between 550 and 900 rpm. I also changed the distributor, plugs, plug cable, changed the AIC, changed the TPS, changed the ECT sensor, changed the AMM, serviced the injectors, cleaned the TB, changed the fuel pressure thing on the fuel rail, cahnged the gasket, changed the fuel relay, changed the radio suppression relay but I tell you this damn idling problem could never go away. I listened to the patern of idling when the A/C is turned off, it idles in a constant wave manner. up and down then up again and down again........ 0(

So next plan is I am gonna pull the head apart and do the grand valve (i think) on this sucker. My mechanic says maybe it would work this time. The emphasis is "MAYBE IT WOULD WORK THIS TIME".

But I would not be holding my breath...

velan

Volvo940GLE, 1991, 16 valve, Kuala Lumpur, Malaysia.

Velan -

HOw about this for an idea: With the a/c on, there is a change that, under normal circumstances, is supposed to help the engine by upping the idle while compressor is engaged. So, whatever that change is, it is somehow having an effect on your engine control system.

The a/c adjustment is different in different Volvo models, some did it with a vacuum change, some with an ECU change. I don't know what your model does, but there is someone out there who does.

Do not spend more until this line of reasoning is exhausted. There is something going on that is connected with whatever the a/c adjustment does.

The cycling between 550 and 900 rpm on a regular basis sounds like electronic "hunting". The system knows 550 is wrong and raises rpm, hits 900 and knows that's wrong so it lowers it, and oer and over. It has lost the ability to set rpm - unless the a/c change is on. Check out the electrics wiring) and electronics (ECU and other systems).

Just my 2-cents-worth. Hope it helps.

Good Luck,

Bob

:>)

at least you'll have pretty shiny valves!

"1990 740 b230f...replaced...air mass meter..."

Hmm. I would have guessed this car to have the Rex-Regina system, no air mass meter.

Throttle body clean? Throttle linkage and switch adjusted? Intake manifold tight?

What does "erratic" mean?

If the problem absolutely started with the head job, then it's unlikely you have a failed part (I didn't say you didn't break a part) and more likely something was installed not quite right.