1990 240sx , rough shaky idle, possible misfire

[newton240sx]

ive had it for about 2 weeks and its always been this way i just never really was too worried about it but it has started to get kinda annoying. when idling it goes from about 600 to a 1000 continuosly but i feel no problem while driving. ive relplaced the spark plug wires. my dad says my spark plugs look good. i was thinking about changing the rotor and messing with the distributor. if anyone has had this problem could you help me out?

[unseenspeed]

sounds like you have a vacuum leak. I would look at the AAV. I have used propane, not lit, and opened it around the intake manifold to see if the engine runs better. This procedure is not recommended if you are unfamilier with propane.

[onosqv]

this common problem can be a million different things. And since you bought the car that way, it's even harder to pinpoint.

Here's something really quick and easy to try:

- car off: unplug the maf sensor- turn car on - does it idle better now?

If it does, check your maf & maf wiring.

FSM is your friend at this point (downloadable via searching here or under one of the stickies).

Other things that have fixed/helped my idle issue:- resetting tps/idle & base timing- changing distributor cap/rotor- fuel filter/checking injectors (they should be 12 ohms or so, at least dohc is)- coolant temp sensor - the one connected to the intake manifold

The 240sx vert I just picked up had misfiring issues @ idle - changed out the maf sensor & rotor/distributor cap - got rid of most of it (still a lil misfire here & there, but not nearly as bad as before).

[newton240sx]

thanx alot man ill try messing with the distributor today when I get home. and ill take off the mass air flow sensor and put it back on and see if that does anything for me. again thankyou alot for your help. i didnt think anyone would ever reply haha

[KG300ZXTT]

IF the idle goes up and down that means that your IACV (idle air control valve) or AAC is trying to adjust idle. I had the same problem I replace d the IACV and the TPS (throttle position sensor).

U don't have to replace new parts just check or clean the old parts.Here is a link that tells You how to clean the IACV zerothread?id=251133

And try to unplug the TPS (the rpm should go up for a few seconds) and go down.

I fixed the problem by replacing both of the parts but i had spare parts. Let me know if this helped.

[newton240sx]

i messed with the MAF and it fixed it im pretty sure. but thankyou for your help