Folks,

Unsure how to describe this.

97 F150 4.2l

I give the truck gas and there is a split second lag in reaction to the engine.

When I hit the gas I hear the intake open and suck in air and the truck takes a split second to react.

Took to a shop and they suggest it is the clips that old IMRP sensor/linkage.

Any ideas? No codes are being throw. I think the truck idles slightly rough. Plugs are good. Other than this the truck runs fine.

 

Hi, I can't tell from your post if you are gently adding throttle or are really stepping on it. If the latter, you are commanding the transmission to shift down and there will always be a lack of response when that happens.

If you're accelerating from a stop, the torque converter isn't going to transmit the power instantaneously to the transmission either. It takes a small amount of time for the impeller to get the fluid moving. Remember, the converter is unlocked when you're stopped at idle, and it acts like a clutch being released when you add power.

If I'm not understanding something (wouldn't be the first time), please elaborate.

- Jack

 

Thanks for the response. It's not the tranny. Although the lag time of the engine response certainly has an effect on takeoff.

I can get the engine to do this when giving gas at the throttle on top of the intake.

Like I said, it's hard to describe.

Give gas, hear loud suction and then a split second delay before engine reacts.

I've also sprayed carb cleaner to find a vacuum leak. No luck. Even cleaned the IAC.

if I gently give gas there is no problem. It's only on a rev.

 

Try cleaning the MAF sensor with MAF cleaner. Is the intake stock with a clean paper filter, and do you have good Motorcraft plugs, wires, and coil pack? Try running a few bottles of Techron through the gas. Check the intake tube in the fenderwell, make sure it's not blocked with debris.

An IMRC problem should trip the CEL and give you a code. IMRC doesn't open till around 2500 rpm under load.

 

@glc

Plugs are not Motorcraft. However I do intend to change to them as I understand they are best for this truck.

I no experience with Fords, only older Chevys and Honda Accorda so I'm not sure what "paper filter" you are referring to. Also, what's it's function?

 

@glc

Do you mean the air filter?

 

Yes, the air filter, is it a dry paper filter or an oiled reusable one like a K&N? Is the intake and air filter box stock? Check the intake from the fender into the box for debris and blockage.

 

Sorry. A little slow. Lol

The filter and such are fine.

 

I'd think poor plug performance would also effect you under load, not just coming off idle. But, if the plugs are not Motorcraft, DO change them. I can't even begin to understand why a different brand plug would be problematic as long as they are the correct heat range, but, it really does seem that Ford engines don't like anything except Motorcraft.

The rough idle characteristic you describe can certainly be caused by a dirty MAF sensor and the environment it lives in. Be careful cleaning the sensor, it is somewhat fragile, I believe.

- Jack

 

Yes, don't touch it, don't even pull it out of the intake tube. Spray it down with the MAF cleaner using a straw in the can nozzle and let it air dry for 15 minutes.

 

Thanks. Ill give it a try.

I don't have a check engine light, would it be prudent to run by Autozone and see if there is a code being set?

Again, Fords are new to me.

 

It would not hurt to check for codes. Considering you can buy a code reader online for 20 bucks, you may want to get one for your toolbox anyway.

http://www.amazon.com/s/ref=nb_sb_no...d2+code+reader

 

I cleaned the MAFS with CRC cleaner. No difference.

I did some researching and found that the fords seem to have this problem of lack response from throttle. Most of what I have read suggest to flash the pcm. However, I can't tell what year models his helps.

Any more ideas?

On a side note, I came across BlueDriver ODB-II reader. Have any experience. Looks pretty cool.

 

so being 18 year old truck and unknown amount of millege is no concern?

 

That's due to software coding in the DBW throttles. Your truck has the cable driven throttle so this would not apply.

Just to make sure everyone is on the same page:

-The truck is in park running at idle.

-You give the engine some throttle via the gas pedal or by hand under the hood.

-The butterfly opens but the engine speed doesn't increase.

-A period of time later the engine speed increases like it should.

What is the overall condition of the truck?

I would start simple and go from there. Clean the throttle body and all the little air ports, vacuum lines etc. I've seen these get gummed up and cause issues. Secondly, verify there isn't a micorswitch that tells the engine the butterfly valve is close. I don't know if the 4.2 has this but some cars do and if it sticks it will cause this exact issue since the engine is getting conflicting signals. Then make sure plugs, wires and coils are up to snuff. I would bet it's one of these things that would cause the truck to idle rough and hesitate but not throw codes. What happens when you drive the truck WOT? If the ignition system isn't up to snuff this will cause misfires and since the engine is running much faster it might throw a code. It takes a good amount of misfires to actually throw a CEL.