Unusual engine behaviour in third

[P156KWJ]

Afternoon, feel a bit daft asking this as I feel like it will be something pretty simple in the end, but here goes.

My S40 (1.9 D, Renault engine) is intermittently behaving weirdly in third. Specifically, when I tried it out on an open road accelerating just a bit more firm than normal, in third, the engine very briefly drops revs for about a second, about at the time to change to fourth. It almost feels like there's some retardation in speed as well, as it's a slight but noticeable jolt in your seat. It then behaves normally again afterwards. Only seems to do it in third, and only intermittently. There seems to be a pattern towards it only happening when it's just come out of slow city driving. For example, during a long drive after a roundabout on an A road to then continue driving at higher speeds, it doesn't fault...

Wondered if it was an air intake issue at first, just seems odd that it's consistently in that gear. Any ideas?

[aldred309uk]

I had gear specific 0ower issues in mine for a while, turned out to be the egr valve messing up somehow. May be the Avenue to look down as I don't know much about it. My egr valve is now blanked off.

[P156KWJ]

Got someone at work to plug their snap-on diag tool in for me, and these were the active codes. (Ignore the Voltage one, it had a new battery not long ago and didn't have the fault cleared).

A new MAF sensor isn't hugely expensive so may throw one of those at it to see if that changes anything.

[aldred309uk]

When diagnosing my issues I disconnected the MAF sensor and the car drove perfectly. I bought a new sensor hoping that would be it but the problem persisted but I had wasted money on a new MAF sensor. Hopefully this helps you save money, my issue was the EGR valve.

[P156KWJ]

I'll unplug the MAF and see what happens and report back... then if I'm feeling brave and have a day free and some spare patience I'll take the EGR valve off anyway to see how dirty it is. Interestingly GSF and Euro don't seem to sell them for this engine!

[aldred309uk]

To diagnose the EGR after replacing my MAF sensor I got a metal coke can, cut off the top and bottom then laid the remaining part out like a flat sheet of paper, but metal. Removed the egr actuator, placed it face down on the metal sheet and traced it out. Cut out the shape and when I refitted the egr actuator I placed the piece of metal between the egr valve and the egr actuator so that it couldn't open it at the wrong time. This totally fixed my problem and I then bought a banking plate off Ebay due to low funding st the time. Has since passed a few MoTs so haven't actually replaced the actuator.

[P156KWJ]

Problem solved!

Tried unplugging the MAF and it made no difference (and to my surprise, no engine management lights were present), so I plugged it back in and put up with it for a bit longer.

Bought a secondhand MAF sensor yesterday and it's working a dream, not only has the bizarre rev drop off in third (and now fourth and fifth) stopped, it seems to generally have lost any sluggishness it had in first (although I'm wondering if that's a placebo effect, being happy the problem is solved...)

Secondhand MAF sensor was from Volvo & Saab breakers in Basford, Nottingham. At £25 +VAT it was worth a try over Euro Car Parts who are £97 minus whatever discount they have on.

Fingers crossed the fault code has cleared, not plugged the Snap On diag tool in yet...

[mcfe]

Not sure how you guys manage this. When I disconnected my MAF sensor for testing, the car starting idling weirdly! Like really weird and bad and I felt it would stall.