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Ok, so I did a trip to the suburbs of Philly last week — 75 miles going and 75 miles back.
Trip notes:
• It was a very hot day, like 88°F or so.
• I keep the car in an underground garage with a good cool temp.
• When I start the car in the morning, it starts right away. At warmup start, the idle goes up to 1200–800-ish for 30 seconds or so, then adjusts slowly and sticks to 950.
• From garage to highway, all good — the idle was always sticking to 950 like a clock.
• On the highway, always good for 75 miles, idle perfect at every single traffic light and gas station.
• Parked the car, went to lunch/strolled with friends etc. for 3–4 hours.
• Started the car to go home, all good — no roughness, idle at 900-ish.
• Back to highway/cruising, all good, idle perfect at every stop at 950 again.
• During the full trip, the oil temp was always at the first white mark (I think 210°F?)
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Yesterday I drove the car again to the city.
Lots of traffic and never able to cruise (1st–2nd gear only). Roughness came back again — but mostly only at the first restart (this is odd).
E.g., I drive 5 minutes — all ok. I stop and restart right away — it gets rough. It’s almost like the “reboot” goes wrong…
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A few days ago I also made a couple of quick tests:
• I removed the oil cap when the car was warmed up, and the car almost dies (which I read somewhere it shouldn’t).
• During the rough idle, I removed the connector of the fuse in the front seat of the Jetronic box — the car died right away.
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My takeaways:
• The temp doesn’t matter much.
• Regardless of whether the engine is warm or not the roughness seems to always happen at restart, never on the first start of the day.
• It feels like cruising (a steady throttle at 2–3K rpm) helps “cleaning.”
• During the roughness period, the muffler POPS a lot — maybe because the mix is too rich?
• It seems something happens when not cruising, which I don’t think is temp-related anymore. Could it be the fuel? Fuel vapors?
• when the rouchness happens is worse at restart and it clears after 15 mins. after that there seem to be a cycle every 10-15 second cycles (15 seconds at 700-ish rpm, 10 second back to 950 ish) (maybe is the ecu reading and adjusting?)
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My next thing to do:
• At this point, I’m gonna buy a new Lambda sensor — which is cheap and im not sure when the prev owner changed it.
• Im gonna buy a rebuilt WUR. mine is 43 yrs old. time to change it no matter what.
• Since im in the upgrade frenzy, i may buy an AFR gauge since at this point i also have to do other works at my mechanic shop next month.
Questions: can someone explains what is actually happeing from the electronic standpoint? i think at this point i knwo how CIS work but this part is missing.
- is it possible the the box in front needs to be replace os it is unllikely? whats indie that box?
- is it possible to totally remove disconenct the o2 senror? i dont need to pass the emission test anymore, so why bother?
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