2005 Corsa 1.4 - idle issue and flat spot

dispossessed

Our car (Corsa 1.4 16 valve Automatic) was running fine until it went in for a timing belt change. It came out running as rough as guts. The garage delivered it to our home otherwise I would not have accepted it back. Hence I only discovered the rough running when I attempted to drive it a couple of hours later.

I took the vehicle back to the garage and they said ""it is nothing that we have done". Coincidences can and do occur but I was unconvinced..

It was also interesting that on both occasions they had it it went in with a full tank of fuel it was returned with the odometer reset and the low fuel light illuminated.....but I digress...

I checked the plugs, found they were not the correct grade and replaced with the correct grade. Result - instantly a 98% improvement.

However whilst it starts cold or hot with ease and initially will idle beautifully, after a couple of minutes it becomes ever so slightly lumpy. Curiously this disappears instantly if I put my foot on the brake or turn on the air conditioning.

Additionally, hot or cold, it also has a slight flat spot upon initial throttle opening. It feels as if someone has blocked the exhaust. As the car is an automatic it occasionally delays a gear change slightly. However it still accelerates normally and top end appears unaffected.

There are no codes.

In addition to the plugs I have also replaced the coil pack, MAF sensor, the valve that goes to the fuel tank (I forget what it is officially called), replaced the fuel filter and air filter. Cleaned the throttle body, idle air control valve and the various hoses. It has since passed an MOT with no advisories - so we might reasonably assume the brake servo hose is probably not leaking etc

I had it subsequently examined by two mobile mechanics (on seperate occasions) - whilst they confirmed what I was saying they could not identify the source of the problem. However neither appeared particularly interested and both were gone after no more than twenty minutes (still billed for one hour's labour however !).

Any suggestions ...?

Thanks,

Carrot007

dispossessed said:

Any suggestions ...?

Find someone competant ann engaging to work on it.

dispossessed said:

It was also interesting that on both occasions they had it it went in with a full tank of fuel it was returned with the odometer reset and the low fuel light illuminated.....but I digress...

The problem appears to be you went back.

(and have an automatic, I hope it was from new as they are usually ragged to death and of no value second hand in this country).

dispossessed

It can be legally prudent to allow the original garage an opportunity to remedy their error.

"Find someone competant ann engaging to work on it." - without allowing an unkown (to me) person the benefit of the doubt how to do so ?

We bought it with 60,000 miles - no problems whatsoever until this episode. Only paid £1800 pounds five years ago so if we only receive scrap value upon resale it is still reasonably cheap motoring.

Ditzy_Mitzy

EGR valve?  My car had slightly similar symptoms when that went, however it's not an automatic so perhaps masked any flat spots more effectively.  

Norman_Castle

Did they fit the plugs? No reason to touch them for a belt change.

dispossessed

Norman_Castle said:

Did they fit the plugs? No reason to touch them for a belt change.

I am aware of that but I asked them to change the plugs at the same time.Ultimately, as I had to remedy that myself I should  have saved my money.

dispossessed

Ditzy_Mitzy said:

EGR valve?  My car had slightly similar symptoms when that went, however it's not an automatic so perhaps masked any flat spots more effectively.  

Thank you for your input.

I plan to remove & clean the EGR valve this weekend.

I can't see how this could have been affected by replacing the timing belt and plugs but on a 16 year old car I cannot see how giving it a clean can do any harm. Hence it is worth investing a couple of hours of my time.

Thank you.

dispossessed

I have succesfully remedied the issue. It ranspired that the plugs I had fitted were also the wrong grade - despite being stated as correct for my engine by the databases of two separate suppliers.

I was fortunate in locating online a manufacturer's data sheet that listed the correct grade as Bosch FLR8LDCU. I fitted a set of these yesterday with the result the car now runs / idles absolutely fine. The cost was £15.95

onlyfoolsandparking

Good result then. I'm no expert on engines but I have heard a few people say fitting wrong plugs caused them a load of problems, especially on some bikes, go figure!

dispossessed

onlyfoolsandparking said:

Good result then. I'm no expert on engines but I have heard a few people say fitting wrong plugs caused them a load of problems, especially on some bikes, go figure!

Very many years ago ( > 50 + years - think BSA Bantams etc) I used to be considered a bit handy as a tuner of two stroke engines. The effects of plugs and points (remember them ?) on engine performance should not be underestimated.

Ultimately, as you say - a good result !