charliemccraney

My car started to idle rough today. It is an 88 305, tbi. Everything else seems fine except the rough idle. I haven't done anything to the car other than drive it for the past 3 weeks. At idle, the roughness feels like a miss. It idles at normal RPM. It drives fine. Coolant temperature, oil pressure, voltage is all normal.

I data logged with tuner pro and the only thing that looks off to my inexperienced self is that the o2 readings are all over the map at idle. I saw readings as low as 39mv and as high as 842mv and everywhere in between. TPS reads .65v during this time. Iac was 18 - 20 steps.

Is this indicative of a fuel problem?

jay173

Mine does the same thing and I notice a change when changing fuel but its still there either way.


I would like to know about this too.

charliemccraney

Mine seems intermittent. This morning, it was back to normal. I hate intermittent problems.

Keith91sub

Could be time for a new O2 sensor. As you know the O2 readings should swing both sides of 470mv. How is the O2 output at other operating ranges of the motor?

charliemccraney

Actually, it does look as erratic while driving. Does it normally swing that mutch? Unfortunately, I never made a log when it was running right.

I'm going to check my fuel pressure this weekend. At 133k, it's entirely possible that the pump could be getting ready to die. I can observe the injector spray pattern.

charliemccraney

Something else that may be related, which has started in the past few months, is that it will sometimes stall almost immediately after it is first started. If I give it gas before it stalls, it will be fine. It only seems to do it on cold startups. After that initial weirdness, everything seems normal. I have not yet tried to solve that. Since it only occurs with cold starts, it can't be the o2 sensor because, if I'm not mistaken, it's not being used at that point.

By chance, I was just reading up on o2 sensors in order to educate myself in preparation for installing fuel injection on my '61 Ford.

It seems that our old fashioned 1 wire sensors tend to last 30k to 50k miles. Mine probably has at least 30k on it. It also says increased fuel consumption, my city mileage is down about 1mpg. Rough idling is mentioned. Hesitation on acceleration, which I have noticed, but is nothing recent, is mentioned. I'll check my records. It may be time for a new o2 sensor.

Keith91sub

A 1 wire sensor is under $20. You may want to look into converting to a 3 wire - they are about $50.

charliemccraney

I just checked my records. The o2 sensor has over 42K miles on it. I think I'll get another. Even if it's not the problem, it's a good time to do it for preventative measures.

I don't want to mess with installing a 3 wire at the time.

Edit: I just checked my shop manual and it recommends that the o2 sensor is changed every 24K. So I'm going to try to find one and replace it this weekend. Who knows, maybe it'll solve the problem.

jay173

you know since where all having this about the same time of year I wonder if they switches to summer gas mixtures at our local gas stations

since it is still cold out some days then the engine would run bad on summer gas in this colder weather

charliemccraney

I replaced the o2. While it didn't fix the problem, my mileage seems to be back where I remember it. It was definitely time for that.

There is also something is rattling around in my muffler. I'm going to go ahead and replace it. It probably won't fix it but it's a known issue and it's annoying.

I didn't check fuel pressure yet. I aparently cut the fittings off of the gauge setup I made for it way back when and just haven't taken the time to make new ones.

jay173

you know how long since you replaced that fuel filter

charliemccraney

About 500 miles ago.

ericjon262

I have an '85 fiero that's having the EXACT same problem mine won't idle at all anymore without giving it some gas. o2 is all over(almost brand new sensor), TPS and MAP are correct, CTS reading correct, new ignition, fuel pump, fuel filter.

charliemccraney

Today, I checked my fuel pressure, timing, and injector spray pattern. Fuel pressure was 11psi, the same as it was 4 or 5 years ago when I last checked. Timing is on the mark. The spray pattern of the injectors is not so great. I can see droplets but both injectors show similar patterns. I'll run a bottle of injector cleaner through and see what happens. If there is no improvement, I'll dig deeper.

blackfrontier

iTrader: (1)

Speaking of a Fiero, I had that issue and a weak coil was causing the computer to try and compensate and dump more fuel into it. Not sure if that could be an issue in this situation?