Engine stumble

Tiny
DREWEMISON
  • MEMBER
  • 2000 OLDSMOBILE ALERO
  • V6
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
Start the car, runs fine, go to accelerate car almost shuts off. Let the engine throttle for a little while. Car runs fine. Happens on rainy and humid days. I have changed plugs and wires, was told to change the coil packs. They had rust on three of six posts. Ran the car again, same problem. Only code is an EVAP leak (small). What else could it be?
Friday, August 31st, 2018 AT 7:09 PM

18 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning.

The first thing I would do is check the fuel pressure. Low fuel pressure will cause this issue.

Another possibility is the EGR valve. If it is partially open it will cause a cold engine hesitation.

Is the check engine light on? If it is, do you know the codes?

Roy

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Check this guide as well, it deals with hesitation

https://www.2carpros.com/articles/engine-hesitates
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Saturday, September 1st, 2018 AT 9:24 AM
Tiny
DREWEMISON
  • MEMBER
  • 3 POSTS
The only code is p442.
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Saturday, September 1st, 2018 AT 11:47 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
This is the description and diagnostics need to be done for this code.

This code has no effect on your current issue.

Roy

SYSTEM DESCRIPTION
The EVAP system includes the following components:
The fuel tank
The EVAP vent valve
The EVAP canister purge valve
The EVAP canister
The fuel pipes and hoses
The EVAP vapor and purge pipes
The EVAP fresh air vent hose
The fuel till cap

The EVAP SMALL LEAK TEST is based on applying vacuum to the EVAP system and monitoring the vacuum decay. The Powertrain Control Module (PCM) monitors the vacuum level via the fuel tank pressure sensor input. At an appropriate time, the EVAP canister purge valve and the EVAP vent valve are turned on, allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved. The EVAP purge valve is turned off sealing the system. A leak is detected by monitoring for a decrease in the vacuum level over a specified time period, with all other variables remaining constant. A small leak in the system will cause DTC P0442 to be set.

CONDITIONS FOR RUNNING THE DTC
DTCs P0443 or P0449 are not active.
No TP, IAT, FTP, ECT, or MAP Sensor DTCs are set.
The system voltage is between 10-18 volts.
The DTC P0440 diagnostic test has passed.
The start-up ECT is not more than 4°C-30°C (39°F-86°F).
The start-up ECT is not more than 8°C (14°F) more than the IAT start-up temperature.
The start-up IAT not more than 4°C-30°C (39°F-86°F).
The start-up IAT is not more than 3°C (7°F) more than the ECT start-up temperature.
The fuel tank level is between 15-85 percent for a 0.040-0.060 inch leak.
The fuel tank level is between 30-85 percent for a 0.020 inch leak.
The BARO is more than 75 kPa.
The IAT is less than 30°C (86°F).
The VSS is less than 80 MPH.

CONDITIONS FOR SETTING THE DTC
A vacuum decay condition indicating a small leak is detected during the diagnostic test.

ACTION TAKEN WHEN THE DTC SETS
The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
The PCM will turn OFF the MIL during the first trip in which the diagnostic has been run and passed.
The History DTC will clear when the PCM turns OFF the MIL.
The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
The following conditions will set DTC P0442:
A loose or malfunctioning fuel fill cap
Damaged EVAP purge or vapor pipes
A damaged EVAP fresh air vent hose
A malfunctioning EVAP vent valve
A damaged EVAP canister
A leaking fuel tank, fuel sender assembly. O-ring, or pressure relief valve
A leaking fuel filler neck or seal

Reviewing the Failure Records vehicle mileage after the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
1. The Powertrain On Board Diagnostic (OBD) System Check prompts you to complete some of the basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable.
15. The EVAP station is pressurizing a sensor that normally reads vacuum. The scan tool reads high pressure at 0 volts and high vacuum at 5 volts. The scan tool can only read a maximum pressure of 6.0 inches of Hg (0 volts), however the EVAP service station can pressurize the system to much higher pressures. The scan tool value should be within 0.5 inches Hg of the specified value.
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Saturday, September 1st, 2018 AT 12:49 PM
Tiny
DREWEMISON
  • MEMBER
  • 3 POSTS
I finally found a pressure gauge. The fuel pump was bad, replaced it and the filter for $348.00 and the cars runs like new again
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Saturday, September 1st, 2018 AT 5:26 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Nice work, we are here to help, please use 2CarPros anytime.

Roy
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Saturday, September 1st, 2018 AT 5:30 PM
Tiny
RLYAMANDA28
  • MEMBER
  • 1 POST
  • 2001 OLDSMOBILE ALERO
  • 83,000 MILES
My 2001 Oldsmobile Alero is having an idle problem I think. When I am at a light or stop sign my car rpm's will will slightly go up then down. When I try to use heat or air the rpm's go up high then down and my car jumps and sometimes it shuts off my car so I cannot use air or heat.
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
First eliminate all vacuum or air leaks in the system. You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
ASHHALLOWICKED
  • MEMBER
  • 2 POSTS
  • 1999 OLDSMOBILE ALERO
  • 156,000 MILES
I own a 1999 Oldsmobile Alero V6 Automatic. Sometimes when accelorating car will act as if I am pushing and releasing the gas feed quickly, for example as if someone was slightly accelerating at a stop light to show off. I have replaced the throttle positioning sensor, all ignition coils, plugs, wires, did an oil change, one month I ran stp fuel system cleaner through and when that didn't seem to help, I went out and bought Lucas fuel system cleaner the following month since I knew it was better quality. I also had diognostics performed at Auto Zone and they also listened to the motor and both checked out fine, besides a code for an o2 sensor which the guy said wasn't even off enough to cause any problems. The check engine light is not on and does not come on when car acts up. Also I am not sure if this is related to the main concern just stated, but sometimes when I start my car the rpm's wont stay up high enough and the car will die out within the matter of one to two seconds, but if I start the car and rev the engine for just a second it stays started. Any ideas?
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Refer to this walk thru link:https://www.2carpros.com/articles/engine-surges
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
ASHHALLOWICKED
  • MEMBER
  • 2 POSTS
Thanks I will work through this list and try to find the issue
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Your welcome-
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
OUT2KAST
  • MEMBER
  • 4 POSTS
  • 1999 OLDSMOBILE ALERO
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
Problem: when ever you accelerate the car especially between 35-45 mph, the car acts likes its out of gas, doesn't die but as you push the accelerator it doesn't respond right away then grabs. As long as you have the accelerator pushed, it runs perfect. When you let off and then push again it kinda bogs then catches. The kicker about that is it doesn't do it all of the time. It bucks and hesitates like it isn't getting enough gas. Highway driving it happens when I let go of the gas then accelerate slowly it will jerk slightly then grab and drive normal. Driving on the road it sometimes bucks alot and hesitates to go. It has never stalled, check engine light came on I took it to the dealer and they replaced the boot to the ignition coil. It did not fix issue.
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
LEOB
  • MEMBER
  • 2 POSTS
I went about this the wrong way, I changed the spark plugs, Wires, Coils, MAP Sensor, TPS Sensor, Cleaned the IAC Valve, cleaned my MAF Sensor, changed my EGR Valve and the Solenoid Purge Valve, I check the Fuel Pressure Regulator and verified all injectors were working, I made sure the filter was good and I replaced the Air filter I verified all Vaccume lines were good and had no leaks! After Hundreds of Dollars and Time Spent I broke down and took it to my Local Dealership! They found out that the Catylatic converter Was clogged and was causing all my issues. I changed that out, and as soon as I did the car ran like new! Check out your Catylatic converter, my car runs like a dream.
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Tuesday, September 4th, 2018 AT 6:41 PM (Merged)
Tiny
OUT2KAST
  • MEMBER
  • 4 POSTS
  • 1999 OLDSMOBILE ALERO
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 91,500 MILES
I have a 1999 Alero that I took to the dealer to fix the hesitation and bucking problem that occurs at random times, probably once a week. They replaced a boot that connects to the ignition pack/coil. That did not fix the problem and they don't know what the issue is. It seems to do it at low RPM driving conditions or if I am on the highway and let my foot off the gas then try to accelerate slowly it will hesitate. It bucks and hesitates like it isn't getting enough gas. Sometime if the car is idleing that is when is bucks like crazy. Please help!
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Tuesday, September 4th, 2018 AT 6:42 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Have the fuel pressure/throttle position sensor and EGR valve checked out.
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Tuesday, September 4th, 2018 AT 6:42 PM (Merged)
Tiny
MUSICIANS
  • MEMBER
  • 1 POST
I had the same problem with my 99 alero. The problem was a vaccum leak, a small hose located right on the front of the motor had worn and split. The issue was that I couldn't see it was split from the front, rather the puncture was on the engine side (facing the motor). Right as you open the hood, look straight down, across from the cooling fans you will see a black rubber fitted hose that connects from the intake to the exhaust manifold. Carefully pull it off (there are no clamps holding it) and inspect it. It costs less than $2 to buy a new hose and replace. While trying to diagnose the problem myself I changed the spark plugs, airfilter, cleaned IAC and throttle body. All this to eventually find out it was a simple fix. Oh well the car runs like new now:-) Goodluck!
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Tuesday, September 4th, 2018 AT 6:42 PM (Merged)
Tiny
KERMIT DEPHRAWG
  • MEMBER
  • 1 POST
  • 2000 OLDSMOBILE ALERO
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 82,333 MILES
I've read a few different posts on various forums and have yet to find a definitive "fix" for my problem.

First off, my Alero has a very rough start sometimes (i.E. Feels like the engine is going to break loose and whole car shakes). This only occurs every now and then.

My main problem, however, is the Alero started hesitating when I'm already in motion. Say 45-50 mph. And when going up hills/inclines.

I've had people say to change the MAF sensor, change the idle, change the fuel pump, change the catalytic converter, etc. I'd prefer to not spend more than necessary, so can anyone tell me if they've had this problem and how they "fixed" it?

Oh, btw, I have NO service lights coming on either, if that helps.

Thanks! Kermit
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Tuesday, September 4th, 2018 AT 6:42 PM (Merged)
Tiny
LEOB
  • MEMBER
  • 2 POSTS
It ran fine within the first mile, then it start to go down from there, NO Power, Bad Gas Miliage, I'd have to floor it to go up a small incline, Hard shifting, all that good stuff. Troubleshoot the issue all the way down to a clogged Catylatic converter. I changed that out and it ran like a dream.
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Tuesday, September 4th, 2018 AT 6:42 PM (Merged)

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