start then stall when cold after vacuum leak fixed-HELPQUICK

[AaronB]

I just had the intake man. gasket replaced which fixed a major vacuum leak. No more hissing, coolant leaking, or rough idle, it did wonders. The only problem is now when I start the thing when it is cold, it cranks for a couple seconds, catches and then immediately shuts down. If I keep my foot on the gas for a little bit, it will eventually idle on its own. Once warm, the problem goes away and runs fine.

The mechanic who fixed the vacuum leak said the computer may be recalibrating the mixture since it has had to compensate for a big leak. He scanned it, no codes came back.

Other than the vacuum leak, I have recently changed the fuel filter, plugs and wires, dist. rotor, TPS. I need help ASAP. Any ideas? Thanks in advance for the help.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[XJNick]

Hi,

What model year and engine type is this Jeep?
In general, make sure there aren't any disconnected electrical sensors or vacuum lines in that area.
I can't really give any further advice without knowing the model, year, and engine

-Nick

[AaronB]

Yeah, I guess that would help. It's a 94GrandCherokee 5.2L V8. Thanks Nick

[XJNick]

Hi,

I don't know a lot about sensors on the V8, but random stalling is often caused by the Crankshaft Position Sensor (CPS).

Since you say it only happens when cold, though, I'd first check the Coolant Temp Sensor (CTS), Manifold absolute pressure sensor (MAP), and Mass air temperature sensor (MAT) for proper operation.

Another thing you may want to look into is if the TPS is adjusted properly, and if the throttle body and Idle air control motor (IAC) passages are clean.

-Nick

	Crank position sensor A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).