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Roadside Jerry
Roadside Jerry, Auto Mechanic
Category: Car
Satisfied Customers: 2948
Experience:  Auto Mehanic 39 years,30 with the NYPD Fleet Service Division
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coil pack..new fuel pump..faulty fuel pressure regulator or injector

Customer Question

Hi my car is having some problems when i start it it starts after a few seconds it sounds like it wants to die out but then goes back regular idle I have to give it some gas in order to go to regular idle it only does that when i start it when im driving it its fine.Ive replaced the coil pack the ignition control module it has a new fuel pump and filter new spark plugs and new throttle control sensor could it be a faulty fuel pressure regulator or injector I dont know let me know what you think I really need some help thank you Christian Santos.
Submitted: 6 years ago.
Category: Car
Expert:  Roadside Jerry replied 6 years ago.

Hello Mr.Aguirre, you may have a dirty throttle body, or a sticking or defective idle air control valve. You can clean the throttle body and throttle plate with a cleaner made for this, use and old tooth brush to clean both side sides the plate, then wipe out with a rag. You can remove the IAC valve and give it a cleaning also. If you still have the problem,replace the IAC valve. Here are some illustrations .I hope this helps ,Jerry.

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Roadside Jerry, Auto Mechanic
Category: Car
Satisfied Customers: 2948
Experience: Auto Mehanic 39 years,30 with the NYPD Fleet Service Division
Roadside Jerry and 24 other Car Specialists are ready to help you
Expert:  Roadside Jerry replied 6 years ago.

Hello Mr Aguire,sorry to hear that the IAC and cleaning didn't fix your problem. I did some searching for similar problems on your model car and found many reasons for the idle problem. You didn't say if it happens only cold or at all times. If cold I found that things like a vacuum leak,to high oil pressure causing pumped up lifters have been found. I will send one of the help requests and what was found.It turned out to be a rare problem that took some time to find. To check your problem out further would require some in depth testing with a scan tool, to check the sensors and fuel trims when this problem occurs. Sorry what I suggested didn't help,it does cure the problem 90% of the time, sending this to try to help you get some direction to the car fixed,no need to hit accept again, Jerry.

1996 Pontiac Sunfire

Engine: 2.4 L / 146 CID / 4 cyl / Gas / DOHC
Fuel: Fuel Injection
Ignition: Distributorless
Trans: 4-speed Automatic Transaxle (Electronic)
Mileage: 141,000 mi
Emissions: OBD-II Compliant
VIN: 1G2JD12T6T

Misc Data: NO Codes
Symptoms: Poor Idle Quality, Hesitation, Surge,
Cuts out, Stall, Misfire, Poor Fuel
Economy
Occurs: Cold, Hot, Idle, After a Hot Soak,
Intermittently
More Info: Test results & repair history included below

_____________________ ORIGINAL MESSAGE _____________________

Argh! This vehicle has been driving me nuts for the last
couple of days. The problem is it only acts up very
intermitantly with NO CODES... What happens is after the
engine warms up to operating temperature it will begin to
stall/cut out down to 300rpm then recover to 900rpm then stall
down to 300rpm and repeat indefinatly. It will do it after a
continuous run from cold to warm, or from a warm restart after
30min-1hour after a shutdown. Cannot perdict when it will do
it. You can rev the engine up to 2000rpm and you can still
feel a slight mis and the engine will buck periodically.

With the engine acting normally I drove it on the highway and
doing 100Kph(55mph) and mashine the accelerator there is no
pickup, just a lot of noise, you have to manually shift the
trany (auto) and you hear what sounds like an exhaust leak
when the engine is reved above 4500rpm under load only. There
is some acceleration but nothing to write home about. There is
better part throttle acceleration at these speeds than at WOT.

I disconnected the iac with the engine idling normally at
900rpm and drove it throught he city with multiple stops and
starts with a 45minute shutdown and restart with no problem.
The engine did stall after it sat and cooled down and tried to
fast idle(3 hour cooling with outside temp at 6^C (44^F).

There is oil leaking from the cam cover and from around the
oil presure sensor boss.

At the time I hooked the scan tool up to it, it behaved
perfectly for over an hour of trying to get it to misbehave.
Even when the idle is surgine the alternator is putting out
13.8V+ at 300rpm, Here is what I have for the only real scan
session:

Idling At 900rpm.

ECT 115^F(Verified w/ Thermometer)

TP Sensor .35V (Operated within Spec)

Baro Pressure 11 in-Hg

LT Fuel Trim -17.2%

ST Fuel Trim 0 - -7% (cycled from 0 to -7%then Reset to zero
and repeated)

Map Voltage 1.37V (operated within spec)

B1S1 O2 Operated Between 300-600mV

B1S2 O2 Operated Between 400-500mV

I have looked at tons of iatn posts from Oil pressure to
timing belt skipping to reflashing the comp. I'm not really
into throwing parts at vehicle untill i'm entirely desperate,
I'm not there...yet! I know iatn's experiance will let me make
the correct choices and repairs.

Thanks in advance, I'll update when I obtain some more
relavent information.

Matthew

___________________ TEST AND REPAIR DATA ___________________

Checked for codes and none were found.

RELATED REPAIR HISTORY

Replaced IAC with known good unit with no change in
drivability. Replaced Ignition Boots, Plugs Were Replaced
Three Years and 40K ago.

______________ COMMENTS ADDED ON Dec 29, 2007 ______________

Thanks For Your Patience. This vehicle came in for unrelated
mintenance and we did the back pressure test. It was perfect.
At idle the gauge was below 0.25psi, at 2000rpm the gauge was
around 0.25psi, and at 4000rpm the gauge was between 0.25psi &
0.50psi. This was done at operating temperature, before and
after the cat, and with the engine running perfectly...for an
11year old quad4!

The noise that is being heard is from the balance shaft chain.
The chain tensioner was broken causing it to vibrate and make
this noise.

Thanks again for all who replied Matthew

____________________________ FIX ___________________________

Thanks to all who replied, I'm with the majority and believe
that there is also an exhaust restriction, but after the
vehicle was repaired the customer chose to take the vehicle
and has not returned yet for the back pressure test.

The problem turned out to be a faulty diode within the
alternator. WHen I looked throught he other IATN posts, others
have had leaking AC current drivability problems. I hooked my
DVOM between the positive battery terminal and alternator case
and recorded these reaedings before replacing. At idle before
the car would surge and idle rough there was 0.050V of AC
current. when the idle began getting rough and cylinders would
start to drop out the AC volts went up to 0.100V, when the
vehicle started to surge the AC Volts whent up to 0.200V, and
when the vehicle would stall the AC volts would rise up to
0.355-0.400AC-V before the engine stalled out. The quality of
the idle was in direct proportion to the amount of AV Current
being produced. If I get the vehicle back to do a back
pressure test I'll update this post with the readings.

Thanks Again.

Customer: replied 6 years ago.
Reply to Roadside Jerry's Post: Hi jerry is Christian my car still does it if its cold or hot thats why I give it a little gas when I start it then it goes back to normal idle.I change the IAC like you said and cleaned the throttle still does the same thing you think it could be fuel pressure or a bad injector I should take it to get scan,you think a pontiac dealer will tell me what it is whats your opinion thanks for responding get back to me when you can thanks.
Expert:  Roadside Jerry replied 6 years ago.
Hello Christian, It could be that the fuel pressure is bleeding of when you shut the engine off. A fuel pressure test would show this. It can be an injector that leaks down or the check valve in the fuel pump. It can also be a pressure regulator that leaks fuel into the vacuum hose. The only way to find the problem is with some testing,it could take around 2 hours to do all the tests that would be needed, they idea is to check the systems involved ,to prove what is working correctly and what is out of specs This will save you from just replacing parts ,hoping to find the problem. A dealer may be a good place to go, or i you can try to find an independent shop that does this type work, If you want to try to find one ,I suggest you look into WWW.IATN.net ,there is a shop finder on the website, on the left side,says Having Car Problems, look to see if there is a member shop in your area, If so or if you go to a dealer, explain to them your exactly what the problem is. You would have to leave the car so they can test it, to feel what is happening. I hope this helps you to get it repaired. Let me know what is found, or if you need any more questions answered on this problem, this question will remain open for you to come back to. Good luck,Jerry.
Roadside Jerry, Auto Mechanic
Category: Car
Satisfied Customers: 2948
Experience: Auto Mehanic 39 years,30 with the NYPD Fleet Service Division
Roadside Jerry and 24 other Car Specialists are ready to help you
Customer: replied 6 years ago.
Reply to Roadside Jerry's Post: Ok jerry im just gonna take it to a shop instead and have them check it out thanks for all your help hey one more thing theres times when I start my vehicle theres a nocking noise coming from the engine it nocks three times and goes away I dont know what it could be any idea?
Expert:  Roadside Jerry replied 6 years ago.
Hello Mr Aguirre, a knock or clicking that goes away after a very short time is usually an oil drain back problem. I would try using the correct AC brand oil filter,since some other brand filters tend to drain back oil out of the filter.This causes a delay for the oil presuure to build up. I would also switch to a 10 w30 oil if you are presently using a 5w30. Thanks for accepting,good luck with the car,Jerry.
Customer: replied 6 years ago.
Thanks for getting back jerry its funny I been always using a fram oil filter and before I never had that nocking noise before thats kinda od to tell you the truth Im ready to sell my car lol!Well thanks for the info jerry.

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