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Discussion Starter · #1 ·
97 Altima GXE 5 speed. 86,393 original miles. (1 owner, 71 yo Man) Picked this bad boy up for 1800. Very clean in and out.

Light was on when I bought it. Car runs great, with no issues.
Had the codes checked at autozone. Codes were P0505, and P0325. Cleared the codes, and 4 days later, solid light came back on. Ran codes again, P0500, and P0325. Print out is as followed:

IAC circuit condition or idle speed higher/lower than expected
ECM has detected that the IAC counts are higher or lower than expected. The Engine speed is not in its expected range.
Probable Cause:
BB1: Vacuum Leak on engine
BB2: Dirty Throttle Body
BB3: IAC motor Defective
BB4: Poor Electrical Connection to the IAC Valve

Knock Sensor Condition
The powertrain control monitors the knock sensor signal for errors
Probable cause
BB1 Knock Sensor Defective
BB2 Check connector and wirinf to sensor
BB3 Engine mechanical condition-knock or rattle in engine
BB4 Low fuel pressure

Ok... The only common denominators is the fuel category. i.e dirty throttle body, and low fuel pressure..

There is no telling when the last tune up was done on this thing if any at all. I had the oil changed the day I bought it, and the light was still on.

Anything you guys suggest I do first? I've read several post about knock sensors and IAC valves, but not one that has the 2 listed together with my listed symtoms which are none to my knowledge. No mis firing,sputtering, stalling at low idle, nothing! Car runs fine, averaging 29.6 MPG on high way.

Any help with this would be great!
Thanks guys!

· Registered
8 Posts
Start with all the basic tune ups stuff. Spark plugs, wires, cap and rotor, air filter, fuel filter, check the timing and the idle speed. Inspect the belts for wear and for the proper tension.

Cleaning the throttle body is very easy and a good first place to start. Just remove the air intake hose and use carb cleaner on a rag to clean the throttle body. Open the valve and clean all around the edges of the flapper. Don't spray cleaner on the throttle body, just on the rag.

The IAC is alot more difficult to take out and clean, but can be done if you have a day to commit to it. Removing the Oil filter helps and getting a 10mm ratching box wrench will help. You need to get to it from below the car. Remove and clean with carb cleaner. You can also check the electrical plug on the IAC to make sure it is tight.

The knock sensor issue could be just that, a knock in the engine. Timing could be off and old spark plugs could cause a problem. I've heard of loose knock sensors causing problems, but the knock sensor is very hard to get to on this car, on the back of the engine below the air intake. You have to virtually pull the engine from the car to get to that sensor.

· Registered
241 Posts
Those two codes are not related. The knock sensor is known to go bad in the Altimas. You'll need to replace that but its a lots of work involved. I have a brand new one for a decent price, if you need one. Send me PM.

For the IACV code, first check the TPS voltage during idling. If its sitting around 0.3-0.7V then something is likely bad with the IACV system.

· Registered
7 Posts
Discussion Starter · #4 ·
Thanks guys for all the replies!

I'm working on all the above.

I also recently discovered a oil leak coming from the front seal.. It only leaks when the car runs. Would this cause any of the codes to pop up?

I think it really came after getting my oil chaned at wal mart.... I know I know.. I was in a hurry, and miles from the house.. Im almost sure they over filled..
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