List,

We have a 98 3.0CL w/automatic trans that has about 130K miles on the odo. Today the engine idle started fluxuating randomly. When sitting at a stoplight, the idle will swing up and down between about 500 rpm and 2K rpm. Once you are on the gas, it drives fine. I did a quick search on "idle" but only had three threads come back.

Any ideas on what to check?

Thanks,

 

My first though is a Vacuum leak. Check your hoses. Possibly put soap and water in a spray bottle and spray gently on hoses. Bubbles indicates a leak.

Idle Air Control (IAC) Valve. You need a service manual (i.e. HELMS) to better diagnose from here.

 

I took the car to my local parts chain Advance Auto Parts and they used the code reader to find a code for bad idle air control valve. I ordered the part through them for about $100 but it was not a part they keep in stock so I'm waiting two days for delivery.

The exact symptoms were that the idle would flux between 1000 and 1800rpm with the gearshift in park (auto trans). While driving, it would be ok with foot on the gas but as soon as you lift off throttle to decelerate, there would be a hard shuddering that would go away if I moved shifter to neutral.

Hopefully this is not too hard to swap out. From the parts diagram, it looks like there are two bolts attaching the part to the throttle body or intake manifold with one electrical plug and one vacuum line.

 

The idle air control valve may just need cleaning. It may be sticking open and not closing. IACV is spring closed, and electric solenoid open, so if it sticks open the idle will go up, unstick and idle drops. If it's accessible it may be worth removing and cleaning w/ throttle body cleaner.

good luck

 

its def the idle air control valve. or your low on coolant/air in iacv. which is what the idle air control valve needs to operate.

 

Ok. We swapped out the IACV with the new one and all is well at this point. As Wilp99 mentioned, besides an assortment of vacuum hoses in the area, there's also a coolant line. Pretty suprising that coolant could be part of the IACV system...

 

the iacv is pretty much like the choke for fuel injection. it uses coolant temperature to determine how much air to let in or not. glad your rollin.

 

apperantly I have the same problem with my 98 2.3 5spd, can someone provide a DIY on cleaning this IACV. Showing where it is and how to disassemble it for cleaning. Sorry Im a noob to mecanical and I don't want to be playing arround in my engine without knowing what it may cause.

 

get TB cleaner. Remove the 2-3 bolts which hold the IACV together to your IM. Spray TB cleaner inside. Spray again and again. Make sure you use chemical resistant gloves. Put IACV back. At first you won't notice a change but after driving the car it will normalize. $100 for a new IAC. Dude u got a great deal. I was quotet $350 for an aftermarket.