I have been talking to a few people about a problem I have when the car is cold. The car boggs down when pulling out and sometimes quits unless I keep the RPM's up above 1500. One opinion is the Bosch sensor don't meet factory specs and is causing the problem. I was told to replace it with a Delco and the problem will go away. I thought it didn't come into play until the ECM went into "closed loop". That being the case and the car being cold, running for less then two minutes, I don't think it's in closed loop. SO, when does the O2 sensor input come into play and has anyone else seen this problem?

I have the Bosch and I don't have that problem at all, in fact, I have better pickup when the car is cold.

I have a Bosch O2 sensor in my car, and there are no problems like the ones you describe. The car hesitates a bit when cold, but it did that with the old O2 sensor, and the hesitation got better after I replaced the O2 sensor, ignition components, and the fuel filter.

If the car won't idle until it goes into closed loop, try this (from the 1985 FSM, preliminary version):
1) check vacuum hoses for splits, kinks, leaks, and proper connection (as shown on emissions label). Check for air leaks at the throttle body, and at MAP sensor. Check the plugs and wires. Check wiring for proper connections, pinches, and cuts.
2) Check throttle linkage for binding, etc.
3) Check ignition timing.
4) Check IAC valve
5) Check alternator output voltage. (should be above 9 V and below 16 V.)
6) Check Park/neutral switch
7) Check injector balance

* * *

If the Bosch sensor didn't meet the spec, I would think that it would cause problems (and possibly set codes) when the engine went into closed-loop operation. When the engine is cold, or in open-loop for whatever reason, the ECM pretty much ignores the O2 sensor.

I hope that helps.

Ed

You shouldn't rush out and replace a Bosch with a Delco 'just because you've got a Bosch'. If you had any of the other 3rd party O2 sensors, well, that would be a different story altogether and you should only replace it with a Delco or a Bosch.

The ECM ignores the O2 sensor until it goes into closed loop mode. If it thinks the O2 sensor is hosed the ECM will switch back into open loop mode and typically, but NOT always, will set a code, then after a while it will again try to switch into closed loop mode.

If you in fact had a bad O2 sensor you'd more likely see reduced gas mileage and when the engine is warm an idle speed oscillating a few hundred RPM every couple of seconds. This is one of those senarios that a scan tool can largely rule out a problem with the O2 sensor in a few minutes.

If you have a constant high idle you should start by looking elsewhere for more likely causes.

Ive been having good luck with Bosch 02 sensors also. They are pricey though.

An oxygen sensor cannot cause this problem because the car is still in open loop operation.

The Bosch sensor is a great quality product.

Phil

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GTDude
OVER 25 years GM experience

Ok, this might sound a bit odd, and I don't know the full electrical explanation behind it but I had a similar problem when I just swapped my tranny. It turns out that the connector was not fully connected to the ECM.

I guess it couldn't hurt to pop off the armrest, try to reconnect the plugs and see what happens. I know its a long shot, but couldn't hurt.

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19 Year Old Fierophile.
--1986 GT Daily Driver, 4:10s, NX 50 Shot, Borla exhaust, ported manifolds, and a few other goodies
--1984 SE 4.9, IMSA spoiler, Duel exhuast, GT rear bumper, Konis, drop spindles, Rear adjustable perch, Poly total kit, Poly cradle bushings, Big front bar, Added rear bar, 11.25" brakes on all corners w/SS hoses, Fancy wheels wrapped w/soft rubber, and much much more.

quote Originally posted by Howard_Sacks: Ive been having good luck with Bosch 02 sensors also. They are pricey though.

??? AutoZone stocks them for about $20.

quote Originally posted by LarryB: ??? AutoZone stocks them for about $20.

I'm on both sides of this. The Bosch 02 sensor for my Fiero was $18.99 at AutoZone. The Bosch O2 sensor for my Escort was $40. Go figure.

Ed

i have 100k miles on my fiero (02 sensor never replaced), i get about 21mpg and this is keeping my foot light on the throttle, should i replace my 02 sensor?
what other factors have a big impact on mileage? (i keep my tires inflated so thats not it, im talking about a big drop from 26mpg to 21mpg). at idle car doesnt sound smooth neither

$20 for bosch 02 sensor, how much are delco? which is more fuel efficient for determining ratio's lean/rich?

Thanks for all the replys. I do concur with the theory that the Bosch is OK and I didn't think it mattered until is went into closed loop. I guess that I will just have to replace the "canortin rod" assembly. That usually fixes almost anything. Anybody else ever replace that thing?? LOL

Oops.

Yeah. I guess they are a bargain. The last bosch sensors Ive bought were heated and expensive for my jeep and my fathers alfa. I know that the alfas was at least $150. I think the jeep one was $70.

I forgot the fiero was nonheated stock.

<quote>quote:Originally posted by Howard_Sacks:
Ive been having good luck with Bosch 02 sensors also. They are pricey though.

??? AutoZone stocks them for about $20.
</quote>