Starts and idles smoothly, will not rev past idle speed but refuses to stall.

[1998RangerXLT]

I came home in my 98 Ranger and noticed it was not running as smoothly as usual. I wouldn't quite call it rough. I parked and went inside. Next day I started it and when I went to put it in drive, everything seemed normal until I pressed the throttle pedal. It would not rev up at all. Neither will it rev past idle speed in neutral. I can press the pedal to the floor or anywhere in its range (except idle) and it will run very rough; it sounds like it's "hunting" but will not stall. As soon as I let it go back to idle position it idles smoothly. It has thrown no codes; I have a scan tool. Neither has the check engine light been on. I am not completely familiar with the parameters in the live data portion of my scan tool, but I noticed that the MAF numbers don't change much when pressing the throttle. It seems to stay around 5.xx grams/second whether idling or opening the throttle. But a search online for MAF symptoms doesn't describe not revving up at all, and seems to say that the ECU can keep it running by using other sensors (limp home mode). So I am asking for ideas. The truck has about 160K miles on it and has always been super reliable. Thanks.

 

[Rearanger]

The main fuel trim for operation is the MAF. If the computer is not reading increased air volume then the injectors will not squirt more. As well the TPS gives the ECU information on throttle opening.

 

[1998RangerXLT]

Thanks. That helps to confirm what I've been thinking.

 

[Waldoduhh]

Yeah id clean the maf with maf cleaner (auto stores have it always) and check that your throttle body valve is actually moving when you move the outer throttle connection. (Im not fancy with the actual terms of said parts, but i think you know what I'm referring to). If I'm understanding though, your saying that when you press the gas pedal it starts bogging down but won't die and won't rev correct?

 

[1998RangerXLT]

If I'm understanding though, your saying that when you press the gas pedal it starts bogging down but won't die and won't rev correct?

Correct. And as soon as I release the gas pedal it returns to a smooth idle. It is hard to start also and usually requires more than one attempt.
I tried cleaning the MAF sensor; no improvement. The scan tool shows the percentage of throttle opening increases when pressing the accelerator, though I didn't check close enough to see if it was a smooth increase. I suspect the MAF sensor needs replacing. I haven't had a chance to look into it yet. I drive it mostly in winter and I have a car for summer driving.

 

[Waldoduhh]

That sounds like its getting more air but fuel output is not responding, meaning the computer isn't detecting a increase in air flow and ergo, no change in fuel injection. Here's what I would do before you spend the money on a new maf sensor to verify. If you have a obd tool that can measure the maf sensor awesosome, but if not, call your local auto junk yards and see if they have your ranger. Go pull the maf from it, hook it up to yours and test it, see if you regain motor function. If so, viola, than you can decide whether to return thelat maf you pulled and buy a new one, or clean the one you pulled and just keep using it. Some might say well that one could be bad too, and yes they may be right, but thats why your able to return what you pull lol, and its a quick diag for those without the fancy snap on scan tools and such. Up to you which route you wanna go.

 

[Waldoduhh]

lord have mercy the typos are real smart phones aint so smart

 

[Shran]

I would be doing a fuel pressure test on the truck - kind of sounds to me like a low fuel pressure issue.

 

[gw33gp]

I suggest also checking the vacuum while idling and when you try to increase rpm. This can give you information that can help determine if a restricted catalytic converter or other exhaust restriction may be the problem.