aquaman788

Have a 97 XJ 4.0. When I crank my car over in the morning, its starts up almost instantly, like it barely even cranks before it fires up. But almost every time I crank it after that during the day, I takes a much longer crank, like 3 to 5 seconds, and the engine runs rough for about 2 or 3 seconds before it starts to idle smooth.

When I start up in the morning, the RPMs will usually rise to about 1200 on initial turnover, quickly drop to 1000, and then after a minute will stabilize at 700 to 750. When I start it after that, the engine will usually try and go straight to around 700 RPM, run rough almost like a misfire for a few seconds, and then stabilize.

Once she's up and running, she runs great; plenty of power, no stalling, smooth idle and acceleration. Just trying to figure out why it will start up fast in the morning with a higher idle, and then struggle to turn over when warm and have a lower initial idle.

Work done so far. replaced fuel pump and filter assembly, upgraded 4 hole fuel injectors, have run a pressure test on the fuel rail and it is holding well, so I don't think its a fuel pressure issue. Also checked the injectors for signs of leaking and found no evidence of such. New spark plugs and wires, inspected and cleaned distributor cap and rotor contact points. Battery is about a year and a half old. New starter. Removed throttle body and IAC valve and thoroughly cleaned both.

I know people often associate long cranks with a faulty crankshaft or cam shaft position sensor, but if that were the case I would think I would have a no start situation or issues when the car is running. Don't think its a heat or vapor lock issue either, I live in Alaska so my engine cools off fairly quick, and even after sitting for 6 hours while I'm at work it will still struggle to turn over.

I have found recently that if I tap the accelerator when it's long cranking that it will fire up and idle smooth right away.

Any ideas you may have are much appreciated. I know there are alot of forums on this issue but none seem to address my particular circumstances.

xj_eep

I had a similar issue before. I found it to be a bad MAP sensor. I did so by pouring a small amount of cold water on the sensor itself when it was idling rough. I sure if this is your problem, but maybe it’s worth a shot.

Edit: Your TPS might be another one to check.

puredrive

I replaced all my crucial sensors still no luck. Still idling at around 750 RPM

bluejeep2001

Next time your warm...disconnect temp sensor in tstat housing before starting, see if it helps. You will throw a code

puredrive

I have installed a new Mopar sensor but I'll give this a shot.

aquaman788

So I went ahead and installed the old original injectors back in, started the car 5 times yesterday throughout the day and didn't have a single hard start. So it looks like it was something with the 4 hole injectors, likely one was leaking into the engine after shutdown.