Hello All-

I know there are zillions of fuel problems discussed, but I haven't run across discussion of what I'm experiencing, so I'm hoping someone will recognize my symptoms or have good ideas about what/how to test.

'92 Volvo 240 wagon, auto. Starts normally cold or warm, but when warm will, after about 5-10 seconds start to idle very badly (400~ rpm) and immediately die if the throttle is even slightly cracked. If I restart, wait 30 - 60 seconds, and let it run in this spluttering state, I'll hear it suddenly recover, going back to a healthy 800 ish rpm with normal power response, etc.. It only happens at start up. The AMM is new (though aftermarket). New fuel pressure regulator, new cyl temp sensor, new in-tank pump, normal sounding main pump, new distributor cap/rotor.

Given the symptoms can I rule out the idle control and throttle pos sensor? Does the in-tank pump have a relay that can fail, then recover after a few seconds?

Thanks for any thoughts!

bruce

Hi,

I would go only with the IAC having a problem sticking at this point. The TPS itself cannot kill an engine.

I will ask you to notice, when starting the engine, to see if it revs itself up beyond its normal idle speed.
It then should drop back and stay there at around 750 rpm. This is how a good IAC is suppose to work every time cold, warm or any difference thereof. The computer holds it.

Upon exhibiting this behavior it means the IAC is controlling all the air.
It cannot have air leaking in ahead of the throttle but after the AMM later.
In other words, a hole in the accordion hose or from flame trap hoses under the manifold. These hoses can allow air to come into the elbow on the throttle control. This effects the AMM just as much.
All cause sputtering.

Now as far as it killing the engine at speed, that changes things a whole lot. The troubleshooting thoughts are going to be in several different territories.

Ignition first but you took care of that.
Next what tells the ignition what to do and when ... the Crank Position Sensor ... known to flake out at times due to age. How old is yours?

The next is the system relay that is turn on by the ICU and ECU that got their signals from that CPS.
A relay can fail on its own from bad soldering inside or overheating. A few seconds of running rough does not necessarily point to it but it’s mechanical. Almost fragile with age. How old is yours?

You changed the pumps out so that leaves one other relay, that’s electronic, located behind the battery. It’s very reliable considering the zillions of times it fires the coil.

It needs its connections and grounds cleaned about every ten years as a good maintenance routine.
It’s is recommended, by no less than a few Bricksters, to replace the heat sink paste between the base plate and the component on it. This might be a little bit of an overkill but the connections and it are out of sight and out of mind. Near a battery doesn’t help.

Look at all of these small items since the symptoms are going in two directions.

That’s about all I can help with from an armchair.

Phil

Hi,


There isn't a separate relay for the in-tank pump.

It sounds like it could be a sticking idle air valve and I suggest you clean it.

I don't see anything in your post that suggests ruling out this valve or the
TPS.

regards,
Peter

Hi,


There isn't a separate relay for the in-tank pump.

It sounds like it could be a sticking idle air valve and I suggest you clean it.

I don't see anything in your post that suggests ruling out this valve or the
TPS.

regards,
Peter

Thanks Peter-

I'll test and clean the idle air valve. I thought it, and the TPS only affected resting idle, but my problem seems to cause the engine to die at any rpm...

Cheers-