I have 93 nissan quest it was running good but time for tune up i changed plugs. cap and rotor after that it ran great then couple months went by and it started running rough when i take off it was sluggish but as i picked up speed it ran better but seemed to be runnning like it was missing . I then changed plug wires still ran bad, so i replaced plugs still ran bad then i changed cap and rotor everything was replaced still runs bad what could it be ?
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I actually had to replace my EGR valve and the gasket. I clean the valve well and reused both. I don't think the gasket sealed well enough though. So I went ahead and got a new valve, gasket and changed them. It runs a lot smoother now.
the problem is not in the plugs , wires , cap , rotor but in dirty injectors or injector controls and wires
use a quality injector cleaner for a few tanks of fuel
ECM controlled cars do not a tune up as the computer does that 60 times a minute so all you need to do is to run the fault codes and fix the faulty sensors
fault codes are being recorded all the time and only the serious engine or transmission faults put the engine light on
Have you changed the plugs lately? You may need a tune up. Change the plugs and wires. Also, check your distributor cap. If you haven't had a tune up in a long time, I would get it done. Make sure you check for a vacuum leak as well. A simple leak can make a car run rough.
Spark plugs, spark plug wires, distributor cap, and distributor rotor. If you replace all of these you would be doing what is called a major tune-up.
A regular tune-up would be just replacing the spark plugs.
You can check the integrity of the plug wires and distributor cap by spraying them with water while the engine is running. If the engine runs ruff, stall, or you see spark arcing from either the wires or the distributor cap than they will need to be replaced.
The distributor rotor always gets replaced when you replace the distributor cap.
You can also spray the coil with soapy water to see if it is leaking as well.
I worked on a '93 Quest last year. Couldn't find out why it wouldn't start. It was the distributor shaft not held onto its rotating gear. The roll pin had come out of the gear on the end of the distributor shaft. When the distributor cap was off, the rotor was turning with the shaft while the engine was cranking. So I thought that was okay. But when I put my finger on the rotor and it stopped turning, that is when I found out the problem. It's a stretch, but maybe the techs missed it. Take the cap off, and if you can spin the rotor either way just by hand, the distributor gear has come loose.
Looks like they really covered a lot. I suppose next they will you to replace the ecu. Good luck.
Its just fouled some plugs again. Need an overhaul. If you just put a valve job on it it will just put more stress on the rings and will need it anyway. Not much you can do except change plugs all the time! God Bless Greg