I noticed a bit of hesitation a month or two ago (as the outside temps dropped below 50F) when coming onto an expressway off an onramp I have to stop at. To get up to highway speeds, I have to lean on the gas pretty hard and it will hesitate a lot between 1200-2000 RPM''s, then pick up and go just fine. Doesn''t always do that.

Tonight while in a horrible snow storm for a 60 mile commute... my average speed was 25-30mph. My RPM''s were very near 1200 RPM''s and I''d be gently gassing it from 1000 RPM''s, at 1200, it would hesitate hard and RPM''s would drop to <500. Then it would lurch and pickup fine. The reason I''m so certain of the RPM range was because it happened about 30 times in my commute tonight.

2006 MGM 4.6L, single exhaust, otherwise well equipped.
K/N filter recently cleaned/re-oiled
40K miles total
Oil change 300 miles ago.
89 Octane (road ranger)
SeaFoam in the tank at least once an oil change.
Fill up every other day from 1/2 tank (drive a lot).
Tank near 1/2 full during current issue.

Owned since 18K miles (March 08) and religious about maintenance.

I filled it back up tonight with 93octane and threw in a bottle of heet. Never noticed this issue before, but this is the first snow with this car, so I don''t have much cause to drive 50 miles at 30mph. Usually clipping along at 75mph for most of it.

Any thoughts? I''d appreciate any input. I''d rather not take it to a shop if I don''t have to considering Christmas is around the corner.

 

it could be water accumulation in the tank (or just a tank of bad gas). there could also be some issue with the idle air control. I''d have the battery/alternator checked just for good measure. did the car come with the 36K warranty or the 50K? if the later, a dealer would fix it for free. you might try pulling the sensors along the intake and cleaning them off and see if that helps. Also, check the vacuum lines to make sure nothing has come loose. And the last idea I have is to make sure the EGR valve isn''t sticking open.

 

36K warranty, so it''s over. Considering how much I drive, I chew through warranties, so I didn''t bother spending the extra 5G''s to extend it to 50K.

Thanks for the tips.

 

I know this is an old thread that I had made, but I could use some help if anyone has any ideas.

I found that the severe hesitation I was having was due to my fuel pump failing. I had it replaced about 15K ago (for around $800). Prior to that, I cleaned my MAFS and replaced the fuel filter, which helped, but it still hesitated pretty bad. After the pump and cleaning, it ran great... until about a month ago (2500 miles).

It hesitates when I try to accelerate pretty hard. In situations like when I'm coming up a short on-ramp. I lay on the gas, it hesitates, stutters a bit, then takes off and runs fine. May still be the MAFS going out or being dirty. Or it's just more noticeable because it's cold out and the air temp is messing it up.

I'll check the air filter and clean the MAFS again since I haven't cleaned either since the fuel pump was replaced. I'll probably also change out the plugs when it warms up a bit since I'm edging up on 75K now.

I can't imagine it's the pump failing again... or at least I'm really hoping it isn't the pump failing again. I don't have any codes being thrown and my CEL isn't on.

The odd thing is that my 1998 MGM with 164K (144K are mine) on it runs and idles more smooth than this car ever has since the day I bought it (with 17K on it).

Any input would be appreciated.

 

nah.. if it hesitates and then goes like a bat outta hell, it's not the fuel pump. You're probably on the right track with the MAF and air filter. You may also have some cloggy fuel injectors as well and need to run some injector cleaner through it. You might also check the plugs and see if they're having a hard time yet.

 

Thanks for the reply. I may mess with it tomorrow. Supposed to be up around 30F... so not real cold.