Something is amiss with my ICE

Several months ago I posted a thread about my MPG dropping from the mid 40's to the low 30's. I purchased a Bluetooth OBDII device and Torque software. I monitored the HV battery every which way and found nothing wrong with it.

My MPGs went back into the 40s after about three tanks of gas and has held there... until recently. About a week ago the 2008 Prius dropped into the low 30's again. As we recently bought a 2015 Prius my lead-foot wife drives that car and I have the 2008 all to myself. I have done every hyper-mile method, that would normally achieve numbers around 50 MPG but all I can get now is 38-39 MPG. So I turned my attention to the ICE behavior and I think that is where my problem may be.

Some things I've noticed:

1) The ICE comes on at times when it shouldn't. The heat/cool system is OFF. The battery is at the green charge level or at least all blue bars. I'm going 35 MPG on a flat stretch of road. The ICE comes on and my instantaneous MPG drops to 25-35. I realize a slight movement of the throttle can cause this but I'm very lightly feathering the pedal to try to keep the ICE from turning on.

2) The ICE MPG is either low (25-35) between 20 and 40 MPG. Getting the ICE MPG to read over 50 is rare.

3) When the ICE shuts off it seems to shutter more than it used to.

4) When the ICE fires up after the car s cold it is noisier than historically.

The car has 160K miles on it. The spark plugs were changed (that was expensive) about 10K miles ago.

The valve clearance adjustment has not been done. While I realize this could impact MPG I doubt it would cause such a dramatic drop. Also if the valves were causing the problem it would be permanent rather than come and go as it has over the past several months.

I have used the Torque app to monitor many things related to the ICE but frankly I can't derive much from those gauges because I don't know what "normal" is so I have no base to compare with.

Any suggestions/help would be appreciated.

 

Thanks. I'll look into those suggestions.

I found a good article on how to do these. I'll do it tomorrow morning. Hope this helps.

Thanks.

To start with I dumped a pint of Seafoam in the gas tank. That stuff really worked for me in a motorcycle.

I was selling my Suzuki, a nearly new bike, and the potential buyer was coming the next day. I rode the bike but the engine was skipping. Wouldn't you know it. It had never done this before and here it is less than 24 hours until the buyer shows up.

I drove to the auto parts store, bought a can (first time ever for me) of Seafoam, went out to the bike parked outside the auto parts store and put about a 1/4 of the can into the gas tank. On the short ride home the Seafoam did it's job and the bike was back to running perfectly.

I don't expect the same behavior in the Prius but I figure it will help.

 

I rejected the gen 4 and we bought a 2015 gen III. The more I read about the gen 4 the less interested I was.

- no spare tire in some models
- slight improvement only in MPG
- white (bathroom fixtures) accents inside
- lower driving position
- I didn't care for the console looks
- lack of 12V outlet on dash
- I don't think the shift lever is in a good place
- smaller glove box
- only one glove box
- lost storage cubbies

Toyota was offering the Gen III for $19K. We just couldn't pass it up. So we bought one. Then tried to decide what to do with the 2008. Edmunds.com suggested it was only worth about $4,500 which wasn't enough for us so we kept it. I just want to get the ICE problem solved.

 

Do you know where I can get a copy of Techstream that runs on Windows 10? The one I have only works on XP and I no longer have XP.

I'll be starting on the throttle body project in a few minutes but I wanted to put something else out here.

Before taking a 14 mile round trip last night I dumped a pint of Seafoam in the gas tank. Before that 14 mile trip my average MPG was reading 39.5 with about 150 miles on the tank of gas. I instantly noticed an improvement in the ICE power and behavior. By the time I reached home the average MPG was up to 41.7, the first time it had been over 40 mpg on this tank. It still could be better though which is why I'm going to clean and lube the throttle body.

 

Well the throttle body was dirty but not sticking and the operation was smooth. I cleaned the butterfly valve and sides of the throat. I then drove the car on another 14 mile trip. Truthfully I didn't notice any improvement from the throttle body cleaning. But the car is behaving much better, not fully up to normal though, having dumped the Seafoam in the tank last night.

I'm wondering if this was all about dirty fuel injectors?

I bought another can of Seafoam at Wal Mart.