Strange loss of power when WOT from dead stop

[98EdBomber]

4.0 SOHC 98' 175K miles

No CEL. Has had a minor idle issue for a while now so Ive been chasing the problem with cheap parts. Its near acceptable so i deal with it at the moment but there are times when it completely smooths out and the idle will be near perfect when i come to a stop at a light for instance. Then at the next light it will go back to vibrating a bit. I can feel it in the floor board and steering wheel when it does this. When it smooths out I can hardly tell its running. Not sure if this is relevant to my current issue though.

It has been serviced at the regular intervals since I bought it when it had 23K on it.


Here is the issue:

For the last, I dont know, maybe year or so Ive noticed that sometimes when Im at a stop light the engine will completely lose all power whenever I mash the pedal instantly down to WOT. It will also do this if I go WOT while starting to round a turn from a dead stop. It completely "dies" (its still running though) and I have no choice but to ease off the accelerator to regain power again.

After that, besides the slightly rough idle, everything is Ok. It gets 18-20 mpg.

In the last year, Ive changed plugs and wires. IAC. Upper and lower manifold or rings. And O2 sensors which have helped. I was getting 14 mpg until the upgrades. But Im still having this specific issue to no avail.

Also, It wont do this when up to speed. Another words, it doesnt lack power unless its this specific condition. Dead stop and WOT = complete power loss.

Very strange and I have read nothing about this issue.

Any ideas? Thanks.

 

[koda2000]

have you changed your fuel filter? have you changed your PCV? have you checked the fuel pressure? have you cleaned your MAF and throttle body?

it sounds a bit strange to me that you seem to often go to WOT from a dead stop (especially while turning). i honestly can't remember the last time i did that and it's not a wise thing to do on an old vehicle, but whatever, it shouldn't fall on it's face when you do.

 

[98EdBomber]

have you changed your fuel filter? have you changed your PCV? have you checked the fuel pressure? have you cleaned your MAF and throttle body?

it sounds a bit strange to me that you seem to often go to WOT from a dead stop (especially while turning). i honestly can't remember the last time i did that and it's not a wise thing to do on an old vehicle, but whatever, it shouldn't fall on it's face when you do.

I understand your concern, but it was just a test to see if it would occur in different driving conditions. I am by no means a crazy driver. Sometimes I am a bit heavy on the pedal from a dead stop but i dont necessarily try to drag race it. It occurs sometimes even with moderate to heavy pedal action and not necessarily complete WOT.

Fuel filter was changed within the last year.

PCV rattles and is in good condition. It is also relatively new.

Have NOT checked fuel pressure yet. Could the regulator be faulty and not be increasing amount of fuel needed while at WOT??? Id think it would throw a code if it was faulty.

Have cleaned MAF and it still did it afterwards.

Throttle body is spotless. This engine runs extremely clean as ive kept up on maintenance.

 

[koda2000]

have you checked the throttle position sensor?

 

[98EdBomber]

have you checked the throttle position sensor?

Not yet? Do I have to check it when the engine is warm?

 

[Sedition]

No, you can check the TPS at anytime.