(It has 220K miles) This started suddenly the day after a painless 450-mile trip – It will run fine for a few minutes, then starts jumping like it’s running out of gas (but it’s not). Then the lurching stops and it runs fine. Repeat . . .etc. New fuel pump 2 years ago; yesterday mechanic changed spark plugs, distributor, crank position sensor . . . but still doing it. Help!
You need to give a better description of the conditions under which this happens. At idle? (How does it idle?) At X speed? Only above/below X speed? Only while accelerating? Only while cruising? Comes and goes if…?
Automatic or manual transmission?
When the mechanic did all of this stuff was the fuel pressure checked?
Thanks for helpful questions (I’ve never done this)! Sometimes idle is a very little rough, but usually fine. Seems to kick in around 2000 rpms, but not consistently. Can be absolutely fine at all speeds (and I think it’s been fixed), or can do it in all gears but 1t (5-speed manual). I will ask about fuel pressure . . . Thanks again,
When was the fuel filter replaced last???
Thanks for the thought – he did that yesterday with the spark plugs and the other stuff
Is there a check engine light involved? If so, what are the exact error codes? (format: “P1234”)
If the plugs/wires/distributor (cap only?)/fuel filter were just replaced and it is still running poorly then here is what I would be doing:
- check fuel pressure under load
- clean MAF sensor, if equipped
- check air intake snorkel for hidden splits/cracks etc.
- put a vacuum gauge on it to check for exhaust clogs / funky valve behavior
- check air and coolant temp sensors
- check compression
- look at oxygen sensor outputs/fuel mix.
Its all busy work that would mostly cost labor time. I’m not a mechanic and I could do all of that in hour. (Compression should have already been done when the plugs were out.
Thanks so much – I passed those on to the mechanic. He said that the error code was for the crank position sensor, which he replaced. . . I appreciate your jumping in with all the ideas! (whole distributor replaced). The weird thing to me is that sometimes it runs perfectly. A frustrating few days!
There isn’t an error code that tells you that the crank sensor is bad. There are plenty of error codes that refer to the crank position sensor - usually to its circuit. I surely hope he didn’t replace the crank sensor for want of a simple wiring fix. A bad/loose connection could easily give you intermittent issues like this, and replacing the sensor won’t necessarily address that - because the sensor itself might be fine.
Here are the basic crank sensor circuit codes:
P0335 Crankshaft Position Sensor A Circuit Malfunction
P0336 Crankshaft Position Sensor A Circuit Range/Performance
P0337 Crankshaft Position Sensor A Circuit Low Input
P0338 Crankshaft Position Sensor A Circuit High Input
P0339 Crankshaft Position Sensor A Circuit Intermittent
There are others that involve the crank sensor circuit (e.g. out of synch with cam). He should spend some more time with the wiring for the CkPS
It was 0335 – so he’s now checking the wiring. You just might be a genius.
Now he’s trying throttle position sensor . . .