Engine rumbling at slow down to stop.

This is not what’s happening. The engine does often stop for long periods of time, I can make it sometimes a mile on just the electric motor, etc. I get close to 40 MPG.

What’s happening, most often during park, is that the engine will rumble like it’s going to shut down and shake the car, then continue running. The engine does still shut down normally and stay off during this cycle.

 

Close to 40 mpg is not really very good at all.....that might be another clue as to what may be wrong.

 

I don’t think the engine would “stumble” due to an older battery, I think the engine would just stay on longer. The mileage has been the same for a number of years without the stumbling issue. I could be wrong, of course, though given that the caulking between my wiper cowlings is gone and Toyota issued a service bulletin regarding coil damage from water intrusion if this caulking is not repaired, I’m leaning towards coils.

In any case I will update when they’re replaced and let you know what happened.

 

Coils will cause misfires and codes. Coils are expensive and it’s a bummer when they make no difference. If you buy cheap aftermarket, keep your old oem coils. A slow shutdown is a slight loss of sync with the transaxle, fairly normal when not fully warm on an occasional basis. Engine running at stops is a sign of a weak hv battery.

 

The engine is not shutting down slowly, it’s stumbling - not shutting down - and continuing to run. The engine only runs a lot at stops when AC is on max due to recent summer heat, but even then it’s not on that much. The engine otherwise starts and stops normally without stumbling.

The coils are original to the car so should be replaced anyway with 172k and factory Densos are $70 each

 

Just realized this is the third gen forum, but I have a 2009. My mistake, please take this into account when reading my above replies

 

I realize you have a gen2. I have had three hybrids including an 08. A gen2 with a good hv battery will never continuously run as you initially stop. A borderline battery might not make 2-3 minutes of stopped engine with AC in 100f weather. When I replaced my 2012 hv battery at 175k miles it was doing better than yours but was weak. I replaced it with oem 5 years ago and immediately the shorter engine off times went away and mpg went back to factory. No playing around with used modules or trying to break the laws of physics with “cycling” modules. Bad coils will code but be my guest and change them.

 

Bad coils don’t always code, I’ve changed some bad ones that didn’t throw a code on other vehicles. I’m not sure of the specifics but I think there might part of the IC on the coils, the support circuitry, not the coil itself, that might have fried out due to water intrusion which might affect some of its sync process occasionally — the stumbling 90% of time only happens in Park.

And I’m not sure where you’re getting that my engine is constantly running. It’s not. Most of the time when the car is stopped at a light, the engine remains off. I only notice this issue when parked for a long time, doesn’t typically happen while driving.

The issue with the wiper cowl weatherstripping was bad enough that Toyota released a document about it, I’m attaching it. The weatherstripping in question has been missing from my car for the last 8 months and since then I’ve driven through numerous heavy rain storms, car washes and etc.

Like I said, not sure if this will solve the problem but “weak battery” as a cause of an engine malfunction that feels like either a momentary lack of spark or fuel before recovery, doesn’t seem like the right answer. Again, though, I’m totally willing to be incorrect

 

And for the record my MPG averages out to 40ish because I do a lot of highway driving at 85 MPH, long distance.

Within the city or non-highway speeds the MPG will often settle at 45-48