bad idle & loss of acceleration

[2.5L4C]

Hi guys, new to the forum and trying to find some experienced help.

I have a 98' 2.5L 4 -Cylinder, manual.

It was doing great, no signs of any issues.

I went to start it in the morning, and it suddenly went into an idle frenzy, very erratic shaking and barely able to stay running. When I push on the accelerator and hold it down, it revs up but then dies out on me over and over. If I try to drive it it has no power.

If I am able to keep it running long enough to warm up after a few minutes, the idle will even out (assuming the 02 sensor kicks in) and it will idle fine. But when I go to accelerate, the same problem exists.


I have replaced the following:

Iac Valve (was throwing a code a month ago)
Throttle position sensor,
Spark plugs (old)
Spark plug wires (old)
PCV valve,
Pcv hose (old)
Throttle body gasket,
Upper manifold gasket (old)
Lower manifold gasket (old)
Dpfe hoses,
Dpfe sensor (looked terrible)
Egr valve,
Front O2 sensor (had pending code)
Air filter,
Fuel injector o-rings,
Cleaned fuel injectors and rail,
Cleaned valves,
Cleaned air intake manifold,
Cleaned throttle body,
Cleaned maf sensor,
Cleaned air temp sensor,


A lot of this stuff needed to be replaced, so most wasnt wasted.

Will be replacing fuel filter today.

 

[2.5L4C]

Also, here is a look at my mass air flow rate (red) alongside my throttle position (green). Is this telling of a bad MAF sensor?

 

[2.5L4C]

Hi guys, new to the forum and trying to find some experienced help.

I have a 98' 2.5L 4 -Cylinder, manual.

It was doing great, no signs of any issues.

I went to start it in the morning, and it suddenly went into an idle frenzy, very erratic shaking and barely able to stay running. When I push on the accelerator and hold it down, it revs up but then dies out on me over and over. If I try to drive it it has no power.

If I am able to keep it running long enough to warm up after a few minutes, the idle will even out (assuming the 02 sensor kicks in) and it will idle fine. But when I go to accelerate, the same problem exists.


I have replaced the following:

Iac Valve (was throwing a code a month ago)
Throttle position sensor,
Spark plugs (old)
Spark plug wires (old)
PCV valve,
Pcv hose (old)
Throttle body gasket,
Upper manifold gasket (old)
Lower manifold gasket (old)
Dpfe hoses,
Dpfe sensor (looked terrible)
Egr valve,
Front O2 sensor (had pending code)
Air filter,
Fuel injector o-rings,
Cleaned fuel injectors and rail,
Cleaned valves,
Cleaned air intake manifold,
Cleaned throttle body,
Cleaned maf sensor,
Cleaned air temp sensor,


A lot of this stuff needed to be replaced, so most wasnt wasted.

Will be replacing fuel filter today.

Fuel filter did nothing.

 

[PetroleumJunkie412]

This is a question for @Dirtman!

 

[Dirtman]

What are the actual codes. Did you do an idle relearn after replacing the tps and iac? Did you use motorcraft parts? Did you clean the maf and throttle body with the correct cleaner? What's the fuel pressure?

 

[2.5L4C]

No codes. Yes to the idle relearn, yes to motorcraft, and yes to the correct cleaner. Haven't taken the fuel pressure, no gauge.

Another tidbit, everything runs great when in limp mode with the maf unplugged.

 

[2.5L4C]

Here is a recent pic of my throttle position alongside my maf.

 

[Dirtman]

What is that graph showing lol. It's useless information without the reference data. Is it reading g/s? If so it's fine for idle but should increase with the throttle input which I'm guessing is in percentage? Actual numbers would be more useful than a graph.

 

[2.5L4C]

Sorry, not familiar with the graph side of things yet. But yes it is showing g/s, idling to slow increase I throttle for the first part and then flooring the throttle the last half.

 

[Dirtman]

Then I'd suspect the maf not reading correct. But it should be throwing a code for it since the computer knows airflow should be increasing as the throttle opens. Maf should go up to 25 g/s or so and stay around 6-8 at idle.

 

[2.5L4C]

Yeah, I expected it to throw a code too but hasn't. So I wrote the maf off. But after narrowing everything I know of down, I'm not left with many other options it seems. It looks to not register the throttle and still thinks it is at idle. Couldn't find much info on what could fail in an maf that would cause it to not register acceleration. But when it comes to the computers and wiring, I'm not too informed. Hate to swap the part as expensive as they are. Will try and get some more obd readings on it

 

[2.5L4C]

Took some more readings. It ended up being the maf sensor. Strange that it never tripped a code.

Thanks for the help!

 

[PetroleumJunkie412]

Thanks for posting the fix!