RPM / Tachometer freaking out

My 96 Blazer has been idling a little rough on and off for the past couple of weeks. I thought it was just bad gas or the fuel filter. I put some 104+ in my tank for the gas and replaced the fuel filter (seemed to run better after that).

BUT.... My problem now is that my truck is stalling and the tach is freaking out. This morning I pulled out of the garage and it stalled in the drive way. Started and it stalled again in the road. Started again the tach shot to 2K then droped, I got to the stop sign and it stalled one more time. I was thinking I was going to have to turn around and get my other truck, but it stayed steady after that... I get almost to where I am going and I am approaching a red light, I notice that my tach is jumping all over the place from 0 (almost stalling) to just about 3K (damn), I pull up to the red light and the tach continues to go nuts, I keep it running by giving it a little gas at 0 so it does not stall out.

Anyone have any ideas as to what this could be caused by, or what may fix it?

I wouldn't recommend run fuel that high in octane in your truck. Race fuels just won't combust until a higher temperature. Doesn't "clean" anything out. Sports cars just need high octane fuel because it won't detonate prematurely and do engine damage.

I doubt this is your problem, but have you tried topping back off with low octane fuel? Where did you get 104+ anyway? High octane fuels will kill your fuel mileage if your car can't combust the fuel properly.

Someone else on here might know more about the idle switches on the car. I had a Honda accord automatic that was running around 2100 rpms when stopped. That was a scary ride lol. I had a bad carb but you don't have a carb on the vehicle I would assume. Maybe your throttle is sticking?

My 96 Blazer has been idling a little rough on and off for the past couple of weeks. I thought it was just bad gas or the fuel filter. I put some 104+ in my tank for the gas and replaced the fuel filter (seemed to run better after that).

BUT.... My problem now is that my truck is stalling and the tach is freaking out. This morning I pulled out of the garage and it stalled in the drive way. Started and it stalled again in the road. Started again the tach shot to 2K then droped, I got to the stop sign and it stalled one more time. I was thinking I was going to have to turn around and get my other truck, but it stayed steady after that... I get almost to where I am going and I am approaching a red light, I notice that my tach is jumping all over the place from 0 (almost stalling) to just about 3K (damn), I pull up to the red light and the tach continues to go nuts, I keep it running by giving it a little gas at 0 so it does not stall out.

Anyone have any ideas as to what this could be caused by, or what may fix it?


I would get a engine capable scanner on it and check out rpm readings in scanner.
post back any codes.
Any check engine lights ?

I wouldn't recommend run fuel that high in octane in your truck. Race fuels just won't combust until a higher temperature. Doesn't "clean" anything out. Sports cars just need high octane fuel because it won't detonate prematurely and do engine damage.

I doubt this is your problem, but have you tried topping back off with low octane fuel? Where did you get 104+ anyway? High octane fuels will kill your fuel mileage if your car can't combust the fuel properly.

Someone else on here might know more about the idle switches on the car. I had a Honda accord automatic that was running around 2100 rpms when stopped. That was a scary ride lol. I had a bad carb but you don't have a carb on the vehicle I would assume. Maybe your throttle is sticking?



The 104+ is the additive I put in to help raise the octane I got from the fuel station; not the actual fuel itself.

My truck will not run good on low octane (regular) I have to run 89-92 (plus-premium) of course the higher the octane the better it runs. If I run anything below 89 it starts knocking at 92 it usually purrs.


I will have the throttle checked, thanks for the suggestion. I don't know if that is it but it is woth a check and hopefull quick fix.

I would get a engine capable scanner on it and check out rpm readings in scanner.
post back any codes.
Any check engine lights ?

Where do I get this engine capable scanner at, or should I just take it in somewhere?

Is the service engine light on?
A good repair shop is best for diagnostic checks..
The good scanners run 3-5K.
AZ can do engine codes but they do not get into data readout.
Good luck
MT

This blazer shouldn't need premium should it? Might that also indicate a problem?

My 96 Blazer has been idling a little rough on and off for the past couple of weeks. I thought it was just bad gas or the fuel filter. I put some 104+ in my tank for the gas and replaced the fuel filter (seemed to run better after that).

BUT.... My problem now is that my truck is stalling and the tach is freaking out. This morning I pulled out of the garage and it stalled in the drive way. Started and it stalled again in the road. Started again the tach shot to 2K then droped, I got to the stop sign and it stalled one more time. I was thinking I was going to have to turn around and get my other truck, but it stayed steady after that... I get almost to where I am going and I am approaching a red light, I notice that my tach is jumping all over the place from 0 (almost stalling) to just about 3K (damn), I pull up to the red light and the tach continues to go nuts, I keep it running by giving it a little gas at 0 so it does not stall out.

Anyone have any ideas as to what this could be caused by, or what may fix it?

I know this is an old post and I should have come back earlier to discuss the outcome. I just wanted to add this in case anyone else comes across this issue.

Well I did take it into a shop and found out that I had water in my gas tank from a previous gas station fill up, which ended up killing my sensor. After dropping and draining the tank and replacing the sensor, my truck has been running just fine since. So I guess I was correct when thinking it was bad gas.