OK, alliteration out of the way, here's the issue: the car is having bogging issue at speed, and sometimes even stalling when coasting or at idle. TBI 350. Car sees A LOT of highway driving. Does it happen constantly? No. Car always has gas. I can go weeks with no issues, or have a really bad day. Today was a really bad day. It was find going into town, but upon restarting it after two hours, it immediately tried to stall, surged to nearly 2000rpms, and then inexplicably and abruptly went back down to around 700rpms, completely outside of any parameters I've ever experienced. I then observed it accelerating on its own (not wot) while coasting. I came to a stop and then the rpms again surged and the car lurched forward; it stumbled a few times, then returned to normal for the rest of my 30 mile journey. The car has no performance issues otherwise. Hot/cold, a/c on/off it can happen. Perhaps unrelated, I have noticed that every now and again, the car will jump up a few hundred rpms while cruising at speed on the freeway, almost as if the torque converter is unlocking and then locking.
Where should I start looking? Idle control valve? Coolant temp sensor? EGR? TPS?
idle control valve and tps would be my starting points, especially since they're easy to check. The stalling could be a misfire, with subsequent overrev being the ICV compensating. However, additional acceleration while cruising sounds like it almost has to be the ICV opening, unless timing is moving around a lot for some reason.
TBI is a pretty simple setup; I'd guess something is just getting gummed up or worn out.
gearheadE30 wrote:
idle control valve and tps would be my starting points, especially since they're easy to check. The stalling could be a misfire, with subsequent overrev being the ICV compensating. However, additional acceleration while cruising sounds like it almost has to be the ICV opening, unless timing is moving around a lot for some reason.
TBI is a pretty simple setup; I'd guess something is just getting gummed up or worn out.
I've had a worn cam/distributor gear cause this too.
Crackers wrote:
gearheadE30 wrote:
idle control valve and tps would be my starting points, especially since they're easy to check. The stalling could be a misfire, with subsequent overrev being the ICV compensating. However, additional acceleration while cruising sounds like it almost has to be the ICV opening, unless timing is moving around a lot for some reason.
TBI is a pretty simple setup; I'd guess something is just getting gummed up or worn out.
I've had a worn cam/distributor gear cause this too.
The dist gear was a common fault on these. Another thing to check is for a vacuum leak at the throttle body gasket.
And EGR sticky or over-delivering. That certainly won't cause the high idle, but until you got to that part of your story, I was thinking EGR valve.
Does this have a manifold absolute pressure sensor? Sounds like a Nissan I had with a bad MAP sensor. Bad sensor was not reading the air right and therfore not giving fuel and or spark correctly.
Link.
Turns out it was a combination of a bad coolant temp sensor and an O2 sensor. They were both just dumping fuel into the system to try and compensate for a cold engine and for a non-present lean condition.
wae
Dork
11/2/16 10:39 a.m.
I hereby award you fifteen internets for coming back and posting the solution to your problem! Future searchers everywhere thank you as they can now see that not only has someone else experienced their problem, but there's something they can try to actually fix it!
I kind of wonder if the coolant sensor went first and the richness of driving around with fuel for -40 degrees in 80 degree weather didn't contribute to the demise of the O2 sensor.
In reply to wae:
Sounds like it. My experience is that the O2 Sensor goes out due to something else messing up.
In reply to wae:
I think you're onto something.
