How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask AMEDEE Your Own Question

AMEDEE
AMEDEE, CHEVY TECHNICIAN
Category: Chevy
Satisfied Customers: 21980
Experience:  ASE MASTER TECHNICIAN ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
279429
Type Your Chevy Question Here...
AMEDEE is online now
A new question is answered every 9 seconds

2004 cavalier: rough idle..Swapped..iac, fuel filter

Customer Question

I have a 2004 cavalier with an ecotec 2.2 and it has a rough idle (500-750) surging idle.
Swapped throttle position sensor, iac, fuel filter, cleaned throttle body, replced plugs, checked fuel pressure (60 psi)
I am lost. still same problems after all this. Any ideas?
After the fuel pump is shut off, it drops pressure fairly quickly, but when running, stays right at 58-60 psi
That shouldnt cause a rough idle though should it?
Submitted: 2 years ago.
Category: Chevy
Expert:  AMEDEE replied 2 years ago.
Hello!

Does the fuel pressure drop down after the engine is turned off?
Customer: replied 2 years ago.

yes. It drops fairly quickly. Down to about 15 within 2 min

 

Expert:  AMEDEE replied 2 years ago.
I would check the fuel pressure regulator. It is located on the fuel rail. It is round, about a quarter size and has a vacuum line going to it. If the regulator is leaking gas than it can cause this problem. Pull off the vacuum line that goes to the regulator. Be absolutely sure there is no gas in the vacuum line. If there is, the diaphragm has ruptured and there is gas entering the engine that is not accounted for and the regulator will need to be replaced!
Customer: replied 2 years ago.

I already checked that. I pulled the vacuum line off of it and no fuel or eveidence that it had been wet at any time. Also pinched the return line and it had the same readings. Could this still be the problem?

 

Expert:  AMEDEE replied 2 years ago.
If you pinched the return line and the fuel pressure continues to drop, then one of the fuel injectors are staying open or leaking fuel. You might want to disconnect the injector connectors or pull up the fuel rail to see which ones are leaking.
AMEDEE, CHEVY TECHNICIAN
Category: Chevy
Satisfied Customers: 21980
Experience: ASE MASTER TECHNICIAN ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
AMEDEE and other Chevy Specialists are ready to help you
Customer: replied 2 years ago.
Wouldnt that give me a rich code or misfire on one particular cylinder? I forgot to mention that I am recieving a p0300 code
Expert:  AMEDEE replied 2 years ago.
YES! It very well should!!
Customer: replied 2 years ago.

It seems to run fine at above idle.. What other possabilities could it be?

Expert:  AMEDEE replied 2 years ago.
The only other thing would be an air or a vacuum leak..
Customer: replied 2 years ago.
so if I pull the fuel rail with injectors attached, and turn the key to run, the faulty injector(s) will be leaking? Correct? I did not see any other places fr vacuum to leak other than the brake booster.. Also, if i put my hand ove the throttle body, it will suck and hold my hand there as it immediately stalls. Could the leaky injector be a small enough leak to not cause a p0301 p0302 etc code?
Expert:  AMEDEE replied 2 years ago.
YES and YES!
Customer: replied 2 years ago.
Thank you so much. I have already accepted answer on previous reply. I appreciate your help. Just one more question. Why would it not give me any problems at acceleration? Is the computer making up for that leak by leaning out the other (correctly working) injectors?
Expert:  AMEDEE replied 2 years ago.
Lets say your computer is bad. Lets say it is holding one of your injectors wide open. It will cause a major issue when the engine is at idle, but will not be noticeable under a load because this amount of gas is normal when accelerating. Make sense?
Customer: replied 2 years ago.
So could it possibly be a computer problem also? How common is that though with the gm's? Do these computers need "flashed"? or can I just swap one from the yard? If I tried one from another car, and wasnt the issue, could I swap the old one back with out any new issues?
Expert:  AMEDEE replied 2 years ago.
YES.. this does happen from time to time. You can check injector pulse on each cylinder with a noid light while the engine is idling. It should blink.. not stay on steady.

I believe the computers do need to be re flashed. I don't think it is plug and play but I could be wrong.
Customer: replied 2 years ago.
Thank you for all your help
Expert:  AMEDEE replied 2 years ago.
You bet!

Have a great day!
Customer: replied 2 years ago.
I pulled fuel rail, with injectors attached, turn key on, fuel pressure raises to 60 but injectors not leaking.
What else could it be?
Expert:  AMEDEE replied 2 years ago.
Something is leaking fuel if the fuel pressure continues to drop.

Did you leave the key on and check for leaks?
Customer: replied 2 years ago.
Yes. Left key in run without engine running. Since injectors are removed. Still drops. If pump check valve leaked back would that still cause rough idle? Just hard fast start? Correct?
Expert:  AMEDEE replied 2 years ago.
YEs.. that is correct. If the injectors and regulator are not leaking when the fuel pressure drops, then yes.. it is back in the fuel tank as long as there are no external leaks. This would only cause a hard start issue..
Customer: replied 2 years ago.
What else could I try?
Expert:  AMEDEE replied 2 years ago.
Check the TPS voltage key on engine off, smoke check the intake system for leaks and disconnect the electrical connector going to the IAC and see if that makes any difference.
Customer: replied 2 years ago.
Which wires on tps? Unplugged iac and engine race sat around 1500
Customer: replied 2 years ago.
K. Found tps voltage at 5.01 v
Expert:  AMEDEE replied 2 years ago.
Hello!

Sorry for the delay!

Are you saying that the idle does not surge any more with the IAC unplugged?
Customer: replied 2 years ago.
It still surges with iac unplugged. Also, I have vacuum coming from port on valve cover
Expert:  AMEDEE replied 2 years ago.
You mean the PCV valve or hose? Will it stop surging if you plug it?
Customer: replied 2 years ago.
The PVC. I removed hose and plugged both PVC and intake port and still surges
Expert:  AMEDEE replied 2 years ago.
Do you have access to a scanner that can read live data?
Customer: replied 2 years ago.
Which data do we need? Tps goes from 7 % to 87 or so at full throttle. Iat reads correct temp.
Expert:  AMEDEE replied 2 years ago.
I want to read the fuel trims at idle to see if they are going rich or lean
Customer: replied 2 years ago.
Reading between -7.81 and -10 on short term. -8.59 on long term
Expert:  AMEDEE replied 2 years ago.
That indicates a rich running condition.

Check the MAP voltage and TPS voltage key on engine off and at idle when the engine is surging.
Customer: replied 2 years ago.
Map reads 57 kpa.
Expert:  AMEDEE replied 2 years ago.
I need to know the voltage reading from both sensors key on engine off and at idle
Customer: replied 2 years ago.
Where is map on this?
Expert:  AMEDEE replied 2 years ago.
Right above the throttle body
Customer: replied 2 years ago.
K. On map, I have black probe on gray. Getting -4.99 on green and -5.01 on red with black stripe
Expert:  AMEDEE replied 2 years ago.
The signal wire is the light green wire
Customer: replied 2 years ago.
5 v between green and gray. 0.0 between green at red/black
Expert:  AMEDEE replied 2 years ago.
IS this with the key on or engine at idle?
Customer: replied 2 years ago.
Key on. Engine off. Sensor unplugged
Expert:  AMEDEE replied 2 years ago.
Ok.. now plug the connector back in and back probe the green wire to get a voltage reading. Start the engine and let me know what the voltage is at.
Customer: replied 2 years ago.
2.7-2.8v on green to red/black
Expert:  AMEDEE replied 2 years ago.
What is the engine vacuum at when the engine is at idle?
Customer: replied 2 years ago.
Where do you want me to "t" from?
Expert:  AMEDEE replied 2 years ago.
Just check the voltage at the hose at the fuel pressure regulator
Customer: replied 2 years ago.
Voltage or vacuum?
Expert:  AMEDEE replied 2 years ago.
Sorry.. my mistake.. typo.. we are looking to get a vacuum reading from the vacuum hose at idle going to the fuel pressure regulator.
Customer: replied 2 years ago.
I have 0 It reads nothing.
Expert:  AMEDEE replied 2 years ago.
No.. when the engine is running. It should read FULL engine vacuum.
Customer: replied 2 years ago.
Coming off intake tube between air cleaner and throttle body is where I tapped. Is that where you wanted me to get vacuum from?
Expert:  AMEDEE replied 2 years ago.
NO.. the vacuum hose going to the fuel pressure regulator.
Customer: replied 2 years ago.
That is the one that goes to pressure regulator. Regulator being mounted on fuel rail with torx bolt ? The vacuum line from that connects to intake tube directly above air temp sensor
Expert:  AMEDEE replied 2 years ago.
So your saying there is no vacuum going to the fuel pressure regulator?
Customer: replied 2 years ago.
Correct. That is what it appears.
Expert:  AMEDEE replied 2 years ago.
This might just be your problem if you are doing it correctly.

Try checking another source to get a vacuum reading. You can use the big vacuum line/hose going to the brake booster.
Customer: replied 2 years ago.
12 inches
Expert:  AMEDEE replied 2 years ago.
Are you sure? It should be much more! If this is the case, then this is our problem. We have a MAJOR air or vacuum leak, timing chain issue or a plugged exhaust.
Customer: replied 2 years ago.
According to my vacuum gauge, I read 12 inches of vacuum at the booster and if I tap the port for the fuel regulator and put my hand over intake tube, I also get 12 inches. If clogged exhaust, why would it run fine on acceleration? Or if skipped time, why would not kick more codes? I checked under valve cover for slack in chain.
Expert:  AMEDEE replied 2 years ago.
You might want to double check or even triple check engine vacuum at another place on the engine or even with another vacuum gauge.
Customer: replied 2 years ago.
Checked again and at vacuum port for evap system directly beside map sensor and vac only to 13 at most. What next? And btw thanks again for the help
Expert:  AMEDEE replied 2 years ago.
You need to smoke check the intake system with a smoke machine. IT is either a major vacuum leak or a engine mechanical issue.

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
< Last | Next >
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
< Last | Next >
  • http://ww2.justanswer.com/uploads/TI/tim37857/2011-10-28_23053_S6301814.64x64.JPG Tim's Auto Repair's Avatar

    Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
  • http://ww2.justanswer.com/uploads/DT/dt69nova/2012-6-15_234154_pic1.64x64.jpg Dave Nova's Avatar

    Dave Nova

    Chevrolet Technician

    Satisfied Customers:

    6870
    ASE Master Certification. GM World Class Certification
  • http://ww2.justanswer.com/uploads/ggrote1/2009-06-27_031011_me.jpg Gary's Avatar

    Gary

    Chevy Technician

    Satisfied Customers:

    5404
    15 years GM master tech
  • http://ww2.justanswer.com/uploads/testedtuff/2009-09-26_170108_pictures.jpg John's Avatar

    John

    Master A.S.E Automotive technician

    Satisfied Customers:

    4071
    A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
  • http://ww2.justanswer.com/uploads/RO/rodcuda/2011-7-25_224114_Donhoff1.64x64.JPG Neal's Avatar

    Neal

    Chevy Mechanic

    Satisfied Customers:

    2306
    Shop Owner and Mechanic on multiple makes.
  • http://ww2.justanswer.com/uploads/goodwrench9124/2008-11-09_220838_dscf0007.jpg goodwrench9124's Avatar

    goodwrench9124

    ASE Certified Technician

    Satisfied Customers:

    2041
    Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
  • http://ww2.justanswer.com/uploads/DR/drivefast1971/2012-1-12_172422_0009051tQKh.64x64.jpg Ron Z.'s Avatar

    Ron Z.

    - Chevy Tech -

    Satisfied Customers:

    1912
    18+yrs experience. State Inspector and Chevy Diagnostics
 
 
 
Chat Now With A Chevy Mechanic
AMEDEE
AMEDEE
2427 Satisfied Customers
ASE MASTER TECHNICIAN ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector