98 Explorer - Cold Starting/ Idle Problem

Often cold idle problems are related to the IAC (Idle Air Control). This is cylindrical item attached to the intake manifold by two screws through a flange on the side of the cylinder. It will have an electrical connector on the rear of the cylinder. You can remove it and clean it and see if this corrects the problem. Or you can just replace it (~$75).

Ed

It may be the IAC valve as posted in the other response, but in all likelihood I'd say your manifold (either upper or lower) gaskets are leaking. If you had work previously done on the front timing chain and tensioner, they should have replaced the lower intake manifold gaskets. Even so, there is no guarantee on the quality of the work. The cold idle problem still existed on my 98 Explorer because the guys at the dealership failed to torque the upper manifold to the lower manifold. Found this out when I replaced the lower manifold gaskets myself because the dealership didn't want to do the job again since they said they did it right! Problem solved. BTW - this mostly applies to the 4.0 SOHC engine.

The manifold gasket was a problem on many of the 98's. I had the problem on my 98 but the symptoms were somewhat different. In my case the car would idle up and then cycle up and down. It would not drop low enough to stall. Your leak might be worse than mine was.

When my IAC started going bad I didn't notice it until the Fall when the weather started getting colder. First symptom was that it took longer to "catch" than normal when starting, but would idle ok after the engine warmed up. After a couple of weeks (maybe a month) it got to where it wouldn't start and idle on it's own without holding the throttle open. I ended up cleaning the IAC valve soon after it got to that point, so I don't know if the problem would have gone away once the weather warmed up. My first "cleaning" lasted a couple of years (I used a throttle body cleaner that was marked safe for coated throttle plates). When it started having problems again I figured it was already on "borrowed" time and tried cleaning it again. I think I overdid it the second time because afterward it started making a trumpeting noise at idle (but it was a smooth idle :-). Replaced it a couple days later a new one from O'Reilly's and that cured the trumpet. Real easy to replace on my '96 OHV V6.

Steve

I have the exact same problem. Was curious if yours is accompanied by a high pitched noise (vaccum leak) as you press/release the gas pedal on smooth hiway. Mine also exhibits this problem, so i thought the two might be related as the other posts also mentioned a vaccum leak.

Mine didn't make any noise until I messed it up with my second "cleaning", and even then it was only at idle, until I opened the throttle a little - it sounded more like a horn than a high pitched noise. However, when it's fairly cold out I do have an intermittent high pitch squeal sound until warm-up, and that varies with throttle opening - usually at about cruising speed on the highway. It doesn't do it all the time, just when the air is pretty cold, and it goes away once the engine is warmed up. When I took it in for that a couple years ago the dealer said it was "throttle plate whistle", had something to do with the material they make the throttle bodies out of these days, and I left it at that. It *has* been doing it more often this winter, so now you've got me wondering if maybe it is some type of gasket leak that closes up after the engine warms up... Thanks!?!? ;-)

Steve