Low Revs??for 10 pts?

Question

I saw this car i was looking to buy yesterday, it was a 1.8 astra coupe x reg..
However when i started the car and tapped the accelerator and let go, obviously the rev counter went up an then down, but the problem is it went below the 1 mark on the rev counter and seemed liked it was going to die out but just before it did the rev counter went back up enough to resume its normal state...
What caused this?am i looking into a problem which is not a problem?should i still buy the car?
thanks

Answer 1

I wouldnt worry bout it at all thats perfectly normal for a simtec engine management system the engine is a cracking engine i used to have a cavalier with the same motor and that did 275,000 miles and was only got rid of cos i got a co car, the problem will be with the idle air control valve bolted on to the throttle bosy assembly common problem you can buy a new one for about £100 or get yours ultrasonically cleaned for about £25

Answer 2

It could be that one of the probes isn't registering properly to the electronic control unit (ECU), e.g. the oxygen sensor (sometimes called "lambda probe"). If this is the case, you're then relying on the measurement of low revs to be picked up before more fuel is added. This typically happens at a lower speed, which would lead to the problem you've described.

In modern engines, the accelerator doesn't control the fuel directly, you're basically just rotating a variable resistor, which is just one of the inputs to the fuel delivery system. The current engine speed, load, gear selection, measurement of air flow and exhaust gases are other inputs. These are all fed into the ECU, which makes a decision on fuel input.

My best guess is that one of the probes is not working properly. It could just be a minor thing, that might affect efficiency in a small way, but it might also cause cut-out while waiting at the lights in winter... Perhaps that's why the car's being sold now. Just a thought.

Answer 3

this is normal behaviour, it sounds like the computer came in to regulate the revs on a cold engine. The Astra engine is a well made long term car good for 150,000 with no major problems. take the car for a drive and I think you will find that it is fine

Answer 4

the air filter could be blocked, take it off and see if it does the same thing (it wont harm the car just to do it for 5 minutes). if it stops then you need a new air filter. if it still does it, check the petrol, i know it sounds daft but if the fuels low and its been sat for a while then it could need a bit of warming up. also, if the car has been sat for a while but has plenty of fuel in, try running it for a while, turn ignition off and leave for 10 mins, then try again. if that stops it then theres no problem. if it carrrys on then dont buy it. there will be an underlying problem that will prob cost you loads.

Answer 5

don't buy the car. There are lots of other cars, including astra coupes. There is clearly a problem with the firing; it might be something as silly as wrong fuel mix, or it might not. Don't buy the car. Wait. A better car will soon appear.

Answer 6

it could be the lambda probe being a bit slow but more likely the idle control valve sticking a little. That, and maybe could do with new plugs.

Even so, if it was clap cold and you suddenly introduce a load of petrol straight after starting the engine, its bound to protest. If it continues to do so when hot, then maybe you've got an issue.

Answer 7

It's perfectly normal for it fall to about 500/600 rpm after revving and then return to tickover at about 800rpm. Try it on any car, they'll all be the same.

Answer 8

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Answer 9

It's probably just the setting of the Idle speed. Had the same problem with my bike and all it took was a turn of a screw!!

Answer 10

It,s most probably the timing ,get the sellers to attend to it ,you,ll also find out what type of future treatment you,ll receive from the sellers - no co-operation == no deal