my 99 2.2 has had a problem on and off for 5 years. 220,000 on clock. when cruising at around 2000 rpms, the motor will start a slight hesitation. if i let my foot off the gas and come to a stop, the rpms will fluctuate and stall. if i punch it, it returns to normal 99% of the time. lately, the slight hesitation sometimes will stop on its own. this problem always starts at cruising speed and never occurs at idle or while accelerating. parts replaced: iac, water temp sensor, fuel filter, egr valve, plugs, wires, tps, map sensor (on firewall) radiator cap, rubber intake bellow. past month noticed water sloshing behind dash. coolant tank not going down. bled cooling system couple times with front end on ramps using radiator funnel. no bubbles in funnel. heater works great and temp just below half on gage. car owes me nothing, but dont want to discard just yet over a possible easy fix. lol. any help appreciated. one of the most reliable cars i've owned.

 

Fuel pump?

 

would a fuel pump work 99 % of the time? when it acts up, punching the throttle usually fixes the problem. and it pulls strong when i punch it. my next step is replacing ecu. does that make sense?

 

Get an ODBII scanner with real time output and find out if the fuel mixture is running rich.

 

I think I would try the fuel pump before ecu, typically cheaper I would think but I haven't look at prices recently.
I also assume no CEL either?
How are the mpg?
What did the plugs look like when they were replaced?
I guess I'm hinting at maybe the car is running rich...

 

no check engine light. mpg's seem lower. plugs done 5,000 ago with 60,000 miles on them. tan, but worn out. changed them because of misfire.

 

going to change fuel pump

 

Fuel pressure is not monitored directly by the computer. The computer would monitor it indirectly via fuel mixture which might set a code based on A/F-02 sensor output. A bad exhaust sensor can also cause issues.

The engine has a fuel pressure regulator bolted to the fuel rail that is controlled by vacuum.

If you think its the ECU get the part number off the current one and find the EXACT part number for the replacement. Shop Ebay or auto salvage yards. Prices range from $20 to $90. Computers seldom go bad but it has happened. If you can find one cheap might consider it.

Any relationship to weather conditions and your problem such as hot or cold temps, rain. Moisture can cause issues with the ign system.

If you had a OBD reader you obtain data when the engine is running OK and when its not then compare. There are also data loggers that will record data for later review.

 

replaced fuel pump friday, no problems today. keeping fingers crossed. thanks everyone.

 

Great! Keep the group informed.