1991 HF Jerks until check engine light comes on

Maybe its coincidental. Some sensors don't come on until the engine is warmed up. And so maybe the problem only occurs when the engine is cold.

And you're still getting code 7 after replacing the TPS? Maybe its out of adjustment.

Or could it be timing?

flash354 said:

Just as the title says I have a stock D15b6 engine and I have an issue where the engine jerks when accelerating very harshly until the check engine light comes on. Once the check engine light comes on it runs perfectly smoothe no hesitations or anything.

The check engine light is code 7.
I've already replaced the TPS sensor.
I think I need to replace the whole throttle body unit but I haven't found the one I need specific for the HF model.

Any other ideas as to what else it could be?

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Did you check the TPS sensor? Not that difficult, just a voltage reading at idle and changing to wot. You can replace the TPS, which sounds like your problem based on the code. Finding an HF TB may be difficult.

I'll go with brittle engine harness for $285 Alex.

I would make sure the TPS is good( tested) before buying one.

If it's good check for calibration. .5v throttle body @ idle position and 5v @ wot.
Make sure the TPS has no dead spots when testing it, you need to sweep through idle to wot but slowly.
Inspect the TPS plug, make sure it' is tight.

How soon does the CEL comes on. Cold engine, normal driving temps?

FYI. There are 2 HF TB's on eBay currently. Used with a price of $150.

mossin_90 said:

If it's good check for calibration. .5v throttle body @ idle position and 5v @ wot.

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0.5V idle, 4.5V WOT. The sensor gets fed 0V (ground) and 5V from the ECU. The half-volt at the ends is used to diagnose electrical shorts, opens and sensor damage. The sensor should never output lower than 0.5V or higher than 4.5V, so the ECU program knows something is wrong if it sees the voltage in those ranges.

The engine stops stuttering once it throws the code because the ECU stops relying on that bad data. The ECU has various degrees of limp-home-mode depending on how important the faulty sensor is.