D15b2 Engine Problems, tachometer misreading

[somedude88]

Ok, to put this out there, I'm under the impression that there could be multiple problems here.

The codes I'm reading on my car are...

Electrical Load
Oxygen Sensor (EVEN THOUGH I REPLACED IT AND RESET THE COMPUTER AND WILL NOT GO AWAY)

Problems that I'm having is service engine soon code will stay off during city driving unless I am in a gear say at a minimum of 1700rpm and higher and I let off the throttle to decelerate rather than using my brakes, after about 15-20 seconds of deceleration it will click on.

That's not what is actually bothering me, if I'm on the freeway going the limit here which is 70 on the freeway, I'll be cruising along throttle response is smooth and accurate, till about 10 or 15 minutes into the drive, then my throttle gets a little unpredictable. If I drive over 80 it will run just fine, same with going 40 - 45 miles per hour.

During this time the engine seems to lose power as if maybe I'm pushing the throttle very little, it seems to be relative to my speed because it behaves in much the same way if I downshift on the freeway to 4th all in the same speed region. So during this I will push the gas a little more.. the engine will seem to be very jerky and will go up and down in throttle, and I know it's jerking my engine around under the hood. If I want to get rid of this all I have to do is decelerate slowly for about 15 -20 seconds to get that service engine soon light to come on and it's all better.

One added detail while this is all happening my tach loves to go nuts, I'll be cruising at 3300 rpms say and it will be waving between 4000 and the actual rpm, sometimes even higher. This is an aftermarket tach, however all this happened before it's installation, this just sort of gives me more information about what's going on, I don't have a stock tach to tell if it's accurate but everything is hooked up correctly and engine behavior has not changed since I installed it therefore no reason to suspect that it is wrong. At any time during this malfunction I can put the pedal all the way down and it will jump to full throttle.

I'm trying to describe this as detailed and organized as possible let me know if you have any questions.

If needed I can supply a video of my tach and speed on my next freeway trip.

Thanks so much for any help, Derek

[91EFbluehatch]

im thinking its an alternator problem??
i may be wrong, but have your voltage checked at a local auto store.

[somedude88]

For more information, if it matters, none of my lights dim or anything.

[freydaddy]

a number of things can make the o2 sensor whack out. but it is still good.
sounds like electrical problem. Ground?
has it been acting like this long? have you done anything new?

[el_jelly]

Ground could be a cause...or something is not connected properly. Have you done anything recently dealing with sensors or wires in the engine? have you clean the engine with water?

the electric load is another problem, I already posted a pic on the procedure to test if it's bad.

[somedude88]

Been like this since I bought it, bought it last summer, never dealt with it, I thought my rusted brake lines, bad tires and bad wheel bearing were a higher priority

[somedude88]

I replaced my pcv valve and it stopped a lot but still does it once in a while and when I let off the gas for a little while it still says check engine soon, no codes anymore since I reset the ecu,I'll see what it will read the next time I drive some distance.