# Rough idle and acceleration below 2.5k RPM. Confused about cause



## Rigguns (Sep 17, 2016)

I don't want to make this a book, so i'm going to try and make this as simple as possible. 
I am driving a 2003 Nissan Maxima GLE with around 125K miles. Never had any real issues with the car before a valve cover crack about 6 to 8 months ago which required new plugs and coils because of an ensuing oil leak. I can't get the statement right now (it's late and I don't want to disturb anyone sleeping because its in my car), but i'm pretty sure the replaced coils were just the 3 on the side of the cracked valve cover. All the plugs were replaced then. Following that work and a tune up, my baby was running better than ever. About 4 months ago, my Maxima sat without any use for a couple weeks, out of nowhere, it took me three efforts to start and on the third the engine finally turned over after I pumped the gas pedal (don't know if that even helped, could just be coincidence) and backfired pretty badly. Got some mixed black/gray smoke out of the back that dissipated immediately after the engine turned over. I only had to move it 50 feet but went ahead and checked fluids, connections, etc and found nothing odd. Since then, it has been going from a rough state that i'll explain below, back to pretty much normal randomly regardless of whether the engine was cold, hot, I had driven it a lot recently, or it had been sitting for a day or two. After that initial bad start and backfire, I've not had any other issues trying to start. My best guess is maybe the other coils that weren't replaced are going bad, the TPS is failing or the wiring has been jostled loose, or my distributor cap needs to be replaced. The mechanic that worked on it after the valve cover is awesome, part prices aren't marked up and his labor costs are minimal, but because of that his garage is packed all the time and I don't have an alternative vehicle so I can't risk leaving mine there for a week for something I may be able to fix myself or get a buddy to fix. 

70% of the time it is running rough:
- Rough idle that shakes the whole vehicle 
- Chugging sound from the engine bay/exhaust rather than that beautiful soft purr
- No shaking/chugging during acceleration until past about 2.5 or 3k RPM then mild shaking
- Can't find ANY indicators that relate to it's random switch between rough and normal 
- From after it started to now (about 4 months) I have only driven it about 4 or 5 days a week at random mileages each time, but almost no change in behavior 
- Service engine light stays on and blinks ONLY during the time that it's running rough, I had my oil changed about 1.8K miles ago

Just yesterday I was running back and forth from Lowes because the Lowes here is crap and I had to get paint remixed 3 times, during those trips (maybe 40 miles total) the vehicle went from rough to normal around 4 times. I don't have a diagnostic tool on hand but I may take it to an autoparts place soon if I can't figure out whats going on. 

I appreciate any help or conjecture.

Edit: I should also mention that the mechanic has been working on my families vehicles for about 10 years. He's trust worthy and does great work. Another option I've considered but forgot to mention is a faulty intake valve timing control solenoid. That may very well be the most likely issue, but I can't get why it keeps switching back and forth like it has.


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## rogoman (Dec 16, 2004)

Since your "service engine" light comes on, the first thing to do is perform an ECU code readout using a portable scan tool to see what fault codes are being set. If you don't have a scan tool, most auto parts stores will do the readout for free. If the car sat without being run for a very long time, the gas may have gone bad or there may be water in the fuel tank.


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## nismolover (Sep 13, 2016)

Rogoman is correct have the code decoded and from there trace the problem.


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