IAC or set me straight!

'99 XJ

I've searched and found a bunch of info but nothing leading me to a definite solution.

Here are the symptoms:
1. 1 out 20 or so attempts to start when cold it won't unless I depress the gas pedal half way a few times while turning over. (yes I know - no gas pedal on start of FI engine...but it gets her going) Once it does catch and start I have to keep giving it gas or it stalls immediatly. After a minute or so of keeping it going with gas pedal the engine "finds itself" and runs at normal idle with no gas pedal assistance.

2. (this one only happened to the wife) She says it seems to be idling high occassionaly. I asked her "you mean like at stoplights and stuff" she said "no, at highway speeds". So I say "well, your not really idling at highway speeds" She then explianed "The engine just sort of seemed to be running faster than it should of all of a sudden when I was going like 60mph. The CE light came on and and the volt guage pegged to the right - then everything returned to normal". So I said "gee that's weird".

3. Maybe related... Sometimes pulling a hard left downhill corner the engine seems momentarily starved of fuel. This happens randomly but I've only noticed it when I have less than 1/8 tank of gas. No CE light or anything when this happens. and it last maybe 2 seconds then everything returns to normal. I was thinking maybe just gas sloshing around in the tank but never had anything like that in another vehicle.

From what I've read on the forum I'm thinking my first check should be the Idle Air Control valve.

Any thoughts?

IACV $45 at AutoZone, 1 yr warrenty...
Some of those symptoms sound like it could be IACV, but I have no idea what would make your voltage gauge peg all the way to the right...? some of it also sounds like something fuel pump related...
I know when I start up in the morning, i turn the key on, but wait a few seconds before i turn the engine over, lets the fuel pump prime and then it starts up immediately...if i don't do that, the starter has to crank for a few seconds, then it finally starts...

It could be a leaking, or leaking fuel injector(s) trying to flood the engine, if so opening the throttle body to add air is getting it closer to the proper A/F ratio for it start. Fuel injector cleaner might help if it is only 1 in 20 starts!

Sounds more like this than a stuck, sticking IAC since it idles normally once it has started.

#2 might be the TPS starting to go bad, developing a bad spot. #1 could also be the TPS starting to develop a bad spot. TPS can testing with a Multi meter, see "Throttle Position Sensor high idle" threads for test details.

#3 could be TPS also, or trash in the fuel tank blocking the intake screen momentarily. As a rule of thumb, one should never drive with less than 1/4 tank of fuel to avoid such potential fuel pump/intake screen problems.

Since the idle eventually corrects itself, my guess would be the power latch relay. It holds the power on to the computer for a few seconds after the key is turned off, allowing the computer to reset the IAC to the starting position. Without this, the IAC is in the wrong position for starting and it is a pain to start and keep running for a minute or so until the computer adjusts itself.

old_man said:

Since the idle eventually corrects itself, my guess would be the power latch relay. It holds the power on to the computer for a few seconds after the key is turned off, allowing the computer to reset the IAC to the starting position. Without this, the IAC is in the wrong position for starting and it is a pain to start and keep running for a minute or so until the computer adjusts itself.

Click to expand...

That is definately a possiblity, but I had the same problems he is having for 2 years and my power latch relay was OK. Also, he has the problem on only 1 out of 20 start up attempts, which makes me think a variable, slightly loose ground can be at least part of his problem. I fixed (replaced) a dozen things on mine and still had the occasional hard start, occasional high or low idle, totally random and cleaning all those grounds was the final solution to really fixing mine.

Of course, it could be a loose conection on the Power latch relay itself.

So, had a problem starting again. Which since last post is now happening a little more frequently - about 1 in 10 starts, was 1 in 20. I removed the IAC. The plunger on the IAC was in an extened posotion. I pushed the IAC in and re-installed. Try to start and it starts right up. In his post "Old Man" thought it might be the power latch relay malfunctioning and not resetting the IAC to its' starting position. Guess that's a possiblity. Trouble is, I cant find any reference to "power latch relay" in FSM or elswhere so I'm not sure where to find it. There are a few relays under the hood and a few interior near feet of passenger. Is it possible the "power latch relay" is called the "automatic shutdown relay"? I'd like to try replacing it and see if this helps. I'm still thinking its the IAC though. When removed the IAC looked a little dirty. Any thoughts?

I'm having similar situation with my 99XJ. The battery is on it's way out too...so I duno if that has anything to do with it, I've been jumping it alot lately. I know, a new battery is in order, but I'm sure there is also another problem to deal with.

It's not stock, it's got headers and the exhaust dumps right after the cat (which I'm changing this weekend, gotta pass inspection). K&N FIPK, so there may be a little more particulate matter getting into the throttle body than if it had a stock airbox. When I start it, sometimes I have to put my foot on the gas (I know, counter-intuitive with FI) to get it to start, but not always. Even when I don't, sometimes it revs up at startup and then just doesn't want to idle correctly. I have to keep my foot on the gas, keeping it at about 1000rpm to get it to idle. Seems like it needs to warm up before it will idle properly. Also, when I'm keeping my foot on the gas, the idle jumps around a bit. Not drastically, probably only changing a hundred or two rpms here and there, but it is noticable. Even when it kicks down and idles "properly" the idle varies a little bit, like maybe +/- 50-100 rpms.

Is this definitely IAC or what?

Anyone got any test procedures to determine if its IAC or the power latch relay thing? TIA

MJMA, my bet is you have an intake gasket leak since you did a header. Tighten the bolts and see if it helps.