Starts fine but sometime wont idle , as long as you hold a little pressure on pedal it runs fine , but when pressure on pedal is relesed it will die , will start right back up and seems when pressure on pedal is slowly released it will idle , and once warm it idles fine . could this be the iac and are they hard to replace , 20 years body work experience so i am handy with tools . thanks for any help.
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Re: 1999 jeep cherokee wont idle cold
The iac would be my first guess but this troubles me as the when the engine is cold all the sensors are ignored until the fuel system goes into "open mode" but to change the iac is simple 2 screws and unplug the module and instructions come with a new one to tell you how far the air pintle is supposed to be set at,
If you can change your own oil than this is easy.
I did rebuild wrecked vehicles for about 15 yrs and gave it up as back in the day we never wore mask's and hacked up to much hardner so now I just fix them,in a chrysler,jeep dealership of course.
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If the start and run fine are on cold starts, I would look for vacuum leaks. The normal start mode for these things is to have a richer condition upon a cold start. When the ECU detects warmth in the engine is drops the extra rich cold start mode then the idle goes rough due to the normal mixture being too lean due to a vacuum leak. Look for cracked, loose or broken vacuum hoses. It could also be due to a EGR valve stuck open.
I have had this happen with the Jeep 4.0 motors because the rubber hoses going to the metal intake from the valve covers had cracks or were broken. Its been a while sine I've been under the hood of a 4.0 but that is a good place to start.
If it will start right back up and if you hold gas pedal will truck stay running ? if it will stay running when you hold the gas then replace the idle air control valve it is bad and cleaning it didnt help. but if it wont stay running even if you hold the gas pedal then the first thing is to make sure you are not loosing fuel presure
it looks like your engine is having an over rich fuel mixture maybe, thatswhy when you press the pedal to the floor it starts becouse you allow lots of air to help clean the mixture while cranking, also you should have black smoke in the tailpipe until it cleans up and runs fine, i think youre having a leak in one our more injectors you should check them first for proper seal under pressure these is done in an injector test machine, second it may be a defective map sensor these trucks some times have a bad map and dont give a MIL (malfunction indacator lamp) and last but more rare to be is a blocked fuel pressure regulator chek fuel pressure it should be between 38 and 45 psi and it shoul hold these pressure when you turn off the engine if pressure drops fast its injector seal problems or fuel pump check
Is it fuel injected or carb??? Try holding the gas pedal to the floor while turning the jeep over. This sometimes makes gas pump thru to the cylinders. Have you changed the fuel filter???? I know alot of jeeps have a fule filter with a bypass back to the tank, and sometimes the filter will be bypassing to the tank instead of the the motor. Check it out?????
its the cold start valve is either stuck or filled up with carbon first take off the hose and spray with carby clean if this doesnt fix it it will have to be replaced.
if you do a search on the net you should be able to find a diagram of where to locate it.
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