Engine only starts if I give it gas and turnover at the same time

[Mcnenc1]

2004 4.0l 42RLE (auto) Sahara

Engine turns over very very slowly. Won’t start up though until I give it enough gas durning the start up and then and only then it will run smoothly.
No rough idling but RPMS drop fairly low while at stop lights?

Any thoughts??

 

[Jerry Bransford]

Your issues sound like a combination of 2 likely problem sources. The first thing I would do is to physically REMOVE both battery connectors from the battery and clean both the inside of the connectors and the battery posts with a wire brush (like comes in a battery cleaner) until they're bright and shiny clean. See if the engine turns over more quickly if that fixes the slow turn over. If that doesn't, your battery is likely either low on charge or it's going bad. Place it on a battery charger over night and see if that fixes it. If not, have it "load tested" by a battery shop to confirm if the battery is good or bad. ONLY a load test can confirm if your battery is truly good or if it's going bad.

The problem of it not idling can be caused by a low battery, true. Especially if you've had to jump start your engine lately. If the battery is good and fully charged by this time and it still idles too low it's likely caused by a dirty IAC (idle air controller). A dirty IAC can be fixed by spraying at least 1/3 of a can of throttle body cleaner into the throttle body while the engine is idling. The IAC will suck the cleaner in through the "idle air control passage inlet" as shown below which is where the IAC gets its air from.

The engine will die when you get enough cleaner into the IAC but just restart it and spray some more. Raising the rpms will cause the cleaner to bypass the IAC. The IAC is what provides all of the engine's air when you're not stepping on the gas pedal. If the IAC is dirty it can stick and provide either too much or too little air causing too high or too low rpms.

 

[Mcnenc1]

Your issues sound like a combination of 2 likely problem sources. The first thing I would do is to physically REMOVE both battery connectors from the battery and clean both the inside of the connectors and the battery posts with a wire brush (like comes in a battery cleaner) until they're bright and shiny clean. See if the engine turns over more quickly if that fixes the slow turn over. If that doesn't, your battery is likely either low on charge or it's going bad. Place it on a battery charger over night and see if that fixes it. If not, have it "load tested" by a battery shop to confirm if the battery is good or bad. ONLY a load test can confirm if your battery is truly good or if it's going bad.

The problem of it not idling can be caused by a low battery, true. Especially if you've had to jump start your engine lately. If the battery is good and fully charged by this time and it still idles too low it's likely caused by a dirty IAC (idle air controller). A dirty IAC can be fixed by spraying at least 1/3 of a can of throttle body cleaner into the throttle body while the engine is idling. The IAC will suck the cleaner in through the "idle air control passage inlet" as shown below which is where the IAC gets its air from.

The engine will die when you get enough cleaner into the IAC but just restart it and spray some more. Raising the rpms will cause the cleaner to bypass the IAC. The IAC is what provides all of the engine's air when you're not stepping on the gas pedal. If the IAC is dirty it can stick and provide either too much or too little air causing too high or too low rpms.

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So it was the battery! Had it swapped and it starts fine. For the IAC it’s so gunked up would you recommend just buying a new IAC or soaking?

 

[Jerry Bransford]

Cleaning the IAC with TB cleaner as described should restore it back to good operating condition.

 

[RMETeeJay]

It's an easy job to clean, just unplug the electrical connectors and remove the 4 bolts holding it on. Torx screws hold on the parts to the body, so if you can remove those you can clean everything thoroughly. Pick up a new throttle body gasket before you start so you can make sure there's no false air getting in underneath.

 

[Jerry Bransford]

It's an easy job to clean, just unplug the electrical connectors and remove the 4 bolts holding it on. Torx screws hold on the parts to the body, so if you can remove those you can clean everything thoroughly. Pick up a new throttle body gasket before you start so you can make sure there's no false air getting in underneath.

That works too but then you also have to clean the orifice in the TB the IAC's plunger fits into. That's why I prefer cleaning it as I described above since it simultaneously cleans both the IAC and its orifice.

 

[Chris]

Glad to hear it wad the battery! Give the IAC a clean and you should be good to go.