Issues related to O2 sensors

[tbondo]

I was wondering what types of issues can be related to faulty or incorrect O2 sensors? I have been trying to track down a high idle and hesitation issue for a while and realized I may have the incorrect O2 sensors installed. I am running a 93 Probe GT ECu (unknown number tag worn off) on my KL-DE from a 97 Probe, but have O2 sensors from a 92 MX-3 GS installed. I did the research and they are in fact different sensors. Was this an oops on my part when I did the swap? I don't get any CEL codes, but I would think they are sending an incorrect signal to the ECU.

[davmac]

Never heard or experienced high idle with bad O2 sensor. Hesitation and bad mpg - but always saw an O2 sensor CEL.

I don't want to make this more complicated then it needs to be but your 97 engine was originally connected to OBD2 ECU. Could some of the sensors - including the O2 be different? Did you swap a K8 coolant pipe over to this engine? How many coolant sensors on your coolant pipe (front of engine)?

I want to believe the high idle problem is really basic issue. If this is a steady high idle just be sure nothing is keeping the TB from completely closing.

[tbondo]

I didn't swap the coolant neck but I did add the second sensor. From what I have noticed most of the sensors and components are the same from the 93 to 97 klde. I have tried a different throttle body assembly with no luck which leads me to believe its something else. I am going to install a different intake tube to rule that out for leaks. I do know the o2 sensors are different but I don't know if those are a contributing factor to my issues. Any input?

[mitmaks]

Start out with simple things, check your TPS adjustment, idle adjustment.

[tbondo]

Yup I have checked the TPS, idle screw, timing, bought a new coolant sensor, and actually swapped out the entire throttle body assembly with a different one. Hasn't seemed to help. So I thought maybe there is a leak somewhere in my intake tube, so I am in process of swapping that out with a custom intake. Another thing I thought of was an exhaust leak from my EGR. The tube from the rear header doesn't seem to be sealing properly into the EGR valve. Could that have some negative affects? I'm just trying everything before I bring it to the Mazda dealer for diagnostics.

[davmac]

I'm assuming this is all KLDE - the the throttle body, IAC and intake. So the IAC is the one with the huge vacuum port that mates with the intake using a very hard to install funny L tube. I do think that if mechanically there is nothing in the way of the throttle plate closing then you do have an air / vacuum leak. Really check over those vacuum lines including that big bugger. It is not unusual for the nipple on the vacuum switches or even the vacuum chambers (those plastic deals under the intake) to crack or break. Also recheck the TPS and set it per the manual with a meter and feeler gauge - it is the only way to know it is set correctly.

You'll soon be expert at removing and installing the intake. Sadly it gets easier but can never be considered really easy or fast. Good luck.

[tbondo]

Yes everything is KLDE. I will have to triple check all the vacuum related items. But I didn't really get my question answered about the EGR leak. That is the last thing I can remember working on when the idle issue started. I'll have to check everything around it. Maybe something plastic broke while working on it. The vacuum chambers you mentioned, can they just up and break on their own? Is that a common problem on these engines? I'm fairly certain that the throttle body,TPS, and IAC are all fine as I have tried a completely different setup and experienced the same issues. I'm still working on the intake tube as I had to relocate some items and ran out of time. Thanks for the input.

[mikeinaus]

check the intake for the pcv on the back of the rear head. its on the back left of the intake manifold. that line looks like it could be prone to vacuum leaks.