The narrowband is no good u need a wideband like aem or innovate. If i was you I would go over the basics check for boost or vacuum leaks. Pretty much all general maintenance stuff make sure everythig is running right. There are tons of threads on stuff to check. Hell even just googling a topic with dsm at the end of it will pull up dsmtuners pretty much everytime.

I'll agree with clipto. The narrowband is useless to actually judge your AFR with. I would check for boost leaks or vacuum leaks.

Throttle Position Sensor is another to keep in mind if you can't find what else is the cause. Commonly overlooked, but I'm pretty sure a bad/mis-adjusted one would throw a CEL that you don't have. Just a thought.

Yeah I know the narrowband is just a cool light but I figure its at least a close guess to what the afr is so it was just weird it randomly started spiking. Found a small boost leak on a split coupler but after replacing it got no change. Orders all new couplers since nowhere local sells 2 inch couplers and I'm going to try out a vacuum and egr delete tomorrow to see if maybe I have a leak in that system somewhere. Thanks for the input guys. Cleane the maf and it got worse so I'm taking that into thought that the maf works and its just a bad vacuum leak somewhere my car idles at 12 on vacuum but it alway has so there is something somewhere letting it out. Having a 96 motor in a 99 body throws alot off even my firing order is all ####ed up

oxygen sensor

It's probably your o2 sensor. Is your check engine light illuminated?

check your coolant temp sensor also. When you unplug the maf it sends the car into a type of fail safe since it has no way of metering air which may make run worse or better, also im pretty sure it is not a good idea to clean your maf. My money is on the coolant temp sensor.

Mr_broadway said:

Having a 96 motor in a 99 body throws alot off even my firing order is all ####ed up

Click to expand...

Did you ever consider that this might be something to look at? How can you expect the members of this sight to tell you which "sensor" is making your car run rich, when you have issues that you already know of.


Having a 96 motor in any year body wouldn't throw a single thing off if it was done correctly.

Definitely do a boost leak and vacumm leak test if you don't know how to YouTube jafro he has great how to videos to point you in the right direction after you verify that you have no boost or vacuum leaks. I would check the front O2 sensor. Also exhaust leaks can give O2 false readings so make sure there are no Exhaust leaks either. All these contributed to my terrible mpgs.

Agree: O2 sensor has some to do with it, but also a stuck open T-stat can do the effect also since the coolant sensor reads a temperature a lot less than what the ECU needs to see to keep the thing in a closed loop condition.

When this happens, the ECU sees that the motor needs more fuel to get the temps up and will tell the injectors to fire in more fuel to solve the condition..and mileage suffers as the results along with a rich condition.

i'd have to agree with the o2 sensor

Lots of guessing with no real diagnosis to begin with.. Run a scanner for any obdII codes, you can even view the o2 voltage signal with better scanners to judge issue with o2 sensor. Boost leak test and go from there so you dont throw parts at the car to see what works.

car had no codes but a coupler days later ran fine and then afte an hour of sitting started to idle like a 280 cam. unplugged the maf and drove it home without hitting 0 on the guage now the car warms up fine but once it hits anywhere above cold it idles rough and breaks up under any kind of boost after boost leak tests and replacing the maf and ecu and upper intake gaskets it still idles bad after initial start. going to swap the transitor tomorrow and see if that clears it up my last and final guess would be a relay because i have literally been through every other part. tps reads fine just as the 02 sensor does and no codes