Hello everyone.
My chevrolet lacetti starts normally with no reving up.But as soon i put it in gear and start driving the rpm go up and down like crazy. In high speeds it doesn’t affect the rpm. And the strangest thing is that if the car is in neutral but moving like on a downhill or just moving slightly on its own the rpms are still reving up and down.
Please help I can’t find anything wrong on it
Thank you
If it is a manual shif, it sounds like a bad clutch, if an automatic, a bad transmission.
Thanks for the reply. Took it out for a spin now after running some tests. Its not related to the clutch i believe. The problem is more obvious now. When i keep my foot on the pedal in neutral at 3000 rpm the engine stalls. Jumping rpms up and down. Did a vacuum leak test all around the engine but nothing. Any other ideas?
Based on this…
… I don’t think that the clutch is the problem.
This is just a wild guess, but I think the crankcase position sensor or the throttle position sensor might be the source of the problem.
Hello there again. I run some more tests today. I disconnected the speed sensor (because like i told you before the fluctuating rpm stopped only when the car was stopped completely)and the engine actually stopped fluctuating the rpm up and down while driving and pressing the clutch. When trying to stop the engine rpm go down normally now with no issues like before. The only problem now is that the engine is surging at low speeds at around 2000 rpm. If i go faster there is no problem. Also if i am in neutral and keeping the rpm at 2000 there is no surging. Now i am even more confused.
Does it happen if ac and defrost are off?
Yes it same with ac off and defrost off
Either a sensor is faulty or unmetered air getting into engine. My guess is either crank pos sensor or leak in payh from air intake to throttle body.
The crank sensor is actually new. And for leaks i tested very well with propane gas. Any other ideas??? Can it be the injectors? Or the throttle body? Head gasket maybe?
I connected back the speedometer sensor and disconnected the maf sensor. I started the engine and the problem almost disappeared. What do you think of that?
I made a test with the maf sensor. While the car is at idle the manifold pressure that the sensor is reading was 50kpa and when i open the throttle the pressure dropped to 20 kpa almost.
I took it out for a spin and the sensor was changing readings so fast that i think it was causing difficulties to the ecu to decide what to do. If is disconnected the car runs much smoother and better with some very light jerking motions which i am guessing they are fron the lack of data from the maf. Also the engine starts much easier with a bit rough idle but corrects itself after a few seconds
Anyone any ideas please?
Hello guys. I have a chevrolet lacetti which is fluctuating rpm very strangely and very high at idle and low speeds. The problem happened after a head gasket replacement. The car has new head gasket. Egr. Crankshaft sensor. Camshaft sensor. Spark plugs. Spark plug wires. Spark plug coil. New gaskets almost everywhere. I tried to find a vacuum leak but nothing. When i connect the code reader it doesn’t find any trouble codes. I did notice though that when i accelerate in neutral that my maf sensor is showing the pressure dropping instead of increasing. I disconnected the maf sensor and the car almost runs normal. It does jerk a bit on low speeds but i am assuming is because it doesn’t have the maf sensor connected. Any ideas what it could be?. Is it a maf sensor faulty? It wasn’t before the head gasket replacement.
Hello guys. I have a chevrolet lacetti which is fluctuating rpm very strangely and very high at idle and low speeds. The problem happened after a head gasket replacement. The car has new head gasket. Egr. Crankshaft sensor. Camshaft sensor. Spark plugs. Spark plug wires. Spark plug coil. New gaskets almost everywhere. I tried to find a vacuum leak but nothing. When i connect the code reader it doesn’t find any trouble codes. I did notice though that when i accelerate in neutral that my maf sensor is showing the pressure dropping instead of increasing. I disconnected the maf sensor and the car almost runs normal. It does jerk a bit on low speeds but i am assuming is because it doesn’t have the maf sensor connected. Any ideas what it could be?. Is it a maf sensor faulty? It wasn’t before the head gasket replacement.