Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
I have a 2001 Nissan Sentra, it's a 1.8 automatic with about 175,000 miles. It idles high and sometimes erratically in park and neutral. It idles low and sometimes stalls while it's in gear. Being cold or hot doesn't seem to make much of a difference and once I get it going, say between 30 - 40 mph, it drives pretty smooth. It's throwing lean condition, IAC valve, and cat codes. These Nissans are pretty well known for having fuel/air ratio issues and from my research I've come to realize there are a ton of different things it could be. So if anybody has experience with these and could point me in the right direction I'd greatly appreciate it.
I'm not a pro, but would pull up fuel trims at idle. If trims are high, rev the engine...if trims go down you proably have a vac leak. Spray some type of spray fuel around intake, injectors, throttle body, etc., see if the trims change. If they go down,theres a vac leak. Then i would smoke test.
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Trouble codes are p0174 (lean condition), p0505 (IAC valve circuit malfunction), and p0420 (catalyst below efficiency)
I got the codes at Autozone, unfortunately I do not have a scanner to pull trim numbers. I understand that the p0505 is probably the underlying issue. But I can definitely start by checking for vac leaks if it's possible that could be the cause of it all.
Vacuum leaks are a good place to start. Gum cutter, brake cleaner & even water will work. Make sure you check between the intake & the cylinder head. Do a visual inspection first. Look at the boot between the air flow meter & the throttle body. Looking for a vacuum leak is the easiest thing to do without a scan tool that displays live data.
So I used brake clean to check for vacuum leaks today. I focused around the intake manifold, the boot connecting the throttle body and MAF, and all the black vacuum hoses I could see. I did not notice a change in the idle anywhere. I also pulled the MAF to clean it and it looked like it had already been cleaned. Guess I will do the old cigar smoke test and maybe pull the throttle body and its components as well to see if they have has also been cleaned. I will report back but in the meantime if anyone has more suggestions just let me know. Thanks in advance.
