O2 sensors causing surging idle

[1slow95]

Last summer I unplugged my O2 sensors because I thought they were causing a problem with the idle. Not surging, but a funny sounding rough idle. I got tired of the car running kind of rough with no O2's, so I bought some new ones early this summer. It definitely seemed to run smoother.

I've had a slight idle surge most of the summer, and it's become really bad recently. It was horrible a couple weeks ago, so I did the idle reset thing. This cleared it up for a while, but after a couple trips it was back to surging. It goes from idle around 750-800 down to 500, then up to 1000 and repeat.

I thought it was a problem with the IAC or IAC tuning for a long time. I even tried my stock 94-95 IAC a couple times, but it didn't help. Finally I found out it was surging even with the IAC unplugged.

So tonight I remove the O2 sensors again and took it for a trip to the gas station, about 15-17 miles round trip. It ran kind of rough and the idle was very rough(it smelled crazy rich), but it stayed steady at 750-800rpms. No surging other than a small dip when you stop.

So what's the problem here? Bad O2's? Bad tune? Something else? The O2 sensors have about 500-600 miles on them.

 

[R.J.]

Buy a Haynes manual and check the O2's with the procedure is chapter 6. With basic tools, there is a way to test almost all of the sensors on the car. You should clean and check your MAF and IAT also. Haynes chapter 6 has great info in it.

 

[Pokageek]

My 02's went bad because my MAF was improperly programmed. I dont care if MAF states its for 42# injectors, they can be waaaay off when you buy them. Then your 02's can go bad within 5 miles or less. That is too expensive to play around with so if you dont have your MAF professionally tuned then get it tuned.

Running rich will destroy them again, in NO time. So they may have been bad from the go or went bad quickly. When I replaced mine the car ran night and day better.

What is your MPG?

 

[1slow95]

It runs much better with the O2's, it just has that surging idle that's making me insane. I had the car professionally tuned 2 years ago, and he did a pretty decent job. There's a couple things I'm not real happy with though, like the hanging idle and low rpm bucking, and I still get a ce light for the EGR even though it's long gone. I plan on having it re-tuned at LaSota some time.

MPG on my last tank was 13. On my last road trip to the drag strip(1/8 mile) I got around 17mpg. (including 8 runs)

It was running rich at idle with the O2 sensors plugged in. Now it's stupid rich at idle. I'll try to reset the computer and see if that helps. And I'll check the fuel pressure, and the other things R.J. suggested.


Will Autozone replace O2 sensors? These can't be more than 6 months old. I think I bought them in April or May.

 

[Pokageek]

Autozone might have a time limit stated on the receipt..you could try though. My 02's are fine and I get 15-17mpg. If they were bad your gas mileage would typically suck.

I had this happen on my 306c.i. and turned out the intake bolts were hand loose..

What about your chip? My tweecer would NEVER seat right on the dam pcm and would do that surge think and sometimes just cut out completely!

 

[1slow95]

I hate taking the pcm out. I know what you're talking about though, mine would cut out all the time at one point because the chip was loose or something. I had it fixed, but it might have come loose again.

I thought maybe the intake worked its way loose, so I tightened all the bolts. I couldn't get to one or two. There were a couple not as tight as the others, but nothing loose.

 

[BlackVert]

i bet your new lasota tune will help

iirc, grady had (final50) had the surging idle thing and figured out what the tweak was that solved it.

i also had the surging idle thing. it went away after i updated my injector timing table to not spray the fuel until after the exhaust valve closes. but i also clocked my maf differently at the same time and changed the intake tube to be a straight shot, which probably also helped. i have a good bit of overlap in my cam.

my mpg currently is around 14 or so in 50/50 highway/city. i'm not driving it much lately, mostly because of that. my camry gets about 25 (but its not as much fun to drive!)

do you have a tweecer?

 

[Pokageek]

I have been in rush hour and still get almost 240miles on a tank.

 

[1slow95]

I have been in rush hour and still get almost 240miles on a tank.

Are you on fumes when you fill up?! I fill up around 1/4 tank, which usually takes 10 gallons. That can be anywhere from 80 miles to 180 miles depending how I drive and where I drive. One time when I was trying to troubleshoot a miss at 5800 rpm's I had to fill up after about 60 miles.


I have a SCT chip, no tweecer. I thought about buying the pro racers package so I can tune it myself, but I'm pretty sure it's way too expensive.

 

[Pokageek]

Well..we have a 15.5 gallon tank IIRC. So you have a good 5 gallons left on 1/4 (the gauge is off I've found..when you are at 3/8's you still have half ). So you are still good for 90 miles.

I am getting no less than 200 no matter what though. I can always go that far.

 

[BlackVert]

lol ... i might get better mileage if i could keep my right foot from snapping my head back and pushing me back in my seat.

but even with the 302, i was happy when i broke 200 miles on a tank. and i typically needed 14+ gallons by then.

keith, is your speedo correct? if your rear end gears make your speedo think you are going 10% faster than you are really going, then your odometer will also say you are going 10% farther than you are really going.

 

[1slow95]

Haven't had time to work on the car, but I did drive it a good bit over the weekend. With the O2's unplugged I get zero surging, even after the car is fully warmed up. The only problem is it's dumping too much fuel at idle and it starts idling rough after a minute or two.