Rough/shakey idle, poor low end tq, What to check next?
2001 Nissan Sentra
1.8L / Automatic
The below are the symptoms of the shakey/rough idle I am trying to resolve. I do not know when the shaking started. This car belongs to my sister and she has not maintained it well.
Shakey/rough at idle. It is worse in drive than in park or neutral and worse in reverse than in drive. The motor has poor off idle torque and seems to lack some power which improves to normal power by 2500-3000 rpm. If the a/c is on it does kick the idle up a bit but the shaking is worse than with the a/c off. From a stop if you stomp the gas pedal the car bogs a bit and acceleration is poor until it gets up to 3000 or so rpm, then it seems to regain most of its strength though I do not know what is truly normal for this motor. The shaking isn’t extremely violent but it is annoying and the off idle/low rpm power lacking. The car always starts right up at first turn of the key. I did run a search on the forum, and a lot came up which I reviewed but I am looking for a more specific answer with regard to these symptoms and what I have already tried.
What has been changed in the past 10k miles:
Cam position sensor
What I’ve checked this past weekend:
EGR – I thought it might have been stuck open a bit, I disconnected the pipe and there was no improvement
Ignition coils – all 4 are sparking. I also pulled 1 at a time with the engine running and each one made the engine stumble so at least I know all 4 cylinders are firing
I’ve replaced the air filter since it looked a bit dirty and I used MAF cleaner to clean the MAF.
Fuel pressure regulator is not leaking internally. I did not see a valve to check fuel pressure.
There do not appear to be any vacuum leaks.
There are no codes stored by the pcm
There is an exhaust leak that appears to be post catalytic converter and the car sounds somewhat like a lawnmower – though not that loud. I will be repairing it but since it is downstream of all o2 sensors/cat I don’t see this as a contributor to the engine shake.
What else I have considered but is difficult to check:
Clogged fuel injectors (they ohm out OK)
Clogged catalytic converter
Clogged inline fuel filter – does the sentra have one or is it strictly in tank
Motor Mounts – seeing how the engine shakes even in neutral (though less noticeably) I don’t see the mounts being the problem.
I'll also be running a compression test tonight. I know she had the water pump replaced not too long ago and I am now suspicious that the car may have overheated and blown the headgasket - though there is no tell tale signs of water in the oil or coolant steam out the tailpipe.
Where should this car idle when warm and the pcm in closed loop and in ‘drive’ – it looks to be as low as 600 rpm. If I use the gas pedal to increase engine speed to ~1000rpm while in gear (foot on brake to prevent rolling) it does not smooth the shaking.
Any ideas on what else I can check or what may be the problem?
Thank you for your replies.
Last edited by jmgtp; Oct 4th, 2010 at 09:36 AM.