Surging/Pulsating throttle when cold

[cnut]

Hi, I have an Alfa 159 1750 TBI

I'm at wits end trying to get to the bottom of the issue I have with my car.

When starting the car from cold and pulling away I can feel a rhythmic pulsing coming from the engine. This progressively gets less and less until it completely clears up a mile later.

It also occasionally misfires from low rpm, high load (3/4 throttle in 4th at 1500rpm etc) this can happen when hot or cold but is more common when cold. Usually when hot it performs faultlessly.

I have Multiecuscan and there are no faults shown. Is there anything in particular I need to be monitoring?

The car has recently been fully serviced, cambelt changed, spark plugs changed etc.

I'm slightly paranoid as the garage I purchased from (Alfa specialist) brought the car cheap as it had a slight misfire. The owner thinks the timing belt had slipped a tooth. So they replaced the valves and fully rebuilt the top end. Really praying this isn't linked to the problem I have!

[GreenV8S]

said:

I can feel a rhythmic pulsing coming from the engine.

This sounds to me like a misfire, especially if the engine feels generally lacking power.

[cnut]

It may well be, but it feels too smooth an action to be a misfire. The car doesn't feel down on power but then I have only recently got it so I have nothing else to compare it to.

[E-bmw]

So, let me get this right, it is a rhythmic pulsing, but is smooth??????

[cnut]

Yes it’s not bucking or anything. Maybe pulsing is the wrong word but the way the power comes in is like a smooth peak and trough that occurs multiple times. But the idle is steady.

[GreenV8S]

said:

the way the power comes in is like a smooth peak and trough that occurs multiple times.

Can you explain that in a bit more detail? Does it drive as though you were moving the throttle pedal, although you're holding it steady? Over what sort of time period does it do it? Is it regular?

[cnut]

Yeah pretty much exactly that. If I hold the throttle steady to accelerate up to 15-20mph in first gear the car accelerates then power drops, accerlates, drops and so on until about a mile. The sensation gradually goes away as the car heats up. I would say it’s at it’s worse the first 30 secs of driving then gets better and better.

It does this every morning and occasionally when the car has been left standing for a couple of hours but not as bad as an overnight start.

[GreenV8S]

said:

I have Multiecuscan and there are no faults shown.

Does that enable you to read the coolant temperature?

[cnut]

Yeah I believe so, are you thinking the coolant temp sensor might be playing up?

[GreenV8S]

The problem seems to be temperature sensitive, so this sensor seems like a good place to start. Also check whether you have a fuel temperature sensor and if so whether you're getting sensible readings from that.

[Elliot2000]

Might be worth disconnecting egr to test it. Slight pulsating with steady throttle can be bought on by a cycling egr valve opening and closin

[cnut]

GreenV8S said:

The problem seems to be temperature sensitive, so this sensor seems like a good place to start. Also check whether you have a fuel temperature sensor and if so whether you're getting sensible readings from that.

Thanks, I will check it out in the morning

[cnut]

Elliot2000 said:

Might be worth disconnecting egr to test it. Slight pulsating with steady throttle can be bought on by a cycling egr valve opening and closin

I'm not sure it has an EGR valve, isn't that a diesel only part?

[cnut]

GreenV8S said:

The problem seems to be temperature sensitive, so this sensor seems like a good place to start. Also check whether you have a fuel temperature sensor and if so whether you're getting sensible readings from that.

I logged the coolant temp this morning and it seems perfectly normal, progressively rising as the car warmed up.

The surging strangely didn't happen this morning but it definitely misfired a couple of times.

What next? Clean MAF out?

[Alzatar]

For the sake of answering this thread that was left dead, for me in my 2011 Astra, the issue was caused by a fuel pressure sensor (also known as a suction control valve in the astra). Replaced with £50 Denso part and problem solved.

[stevieturbo]

Alzatar said:

For the sake of answering this thread that was left dead, for me in my 2011 Astra, the issue was caused by a fuel pressure sensor (also known as a suction control valve in the astra). Replaced with £50 Denso part and problem solved.

totally irrelevant, and the SCV is not a sensor, it is an actuator.

[LucasGT]

Sounds like an air leak to me. Could be a vacuum pipe for the bakes or somewhere on the emissions side but drawing air where it's not needed will confuse the engine management, especially when cold and a slightly richer mix is needed.

Lucas.