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BOBBYSS
BOBBYSS, Master Technician
Category: Chevy
Satisfied Customers: 17409
Experience:  ASE MASTER CERTIFIED, AA DEGREE AUTO/DIESEL TECH
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Gary you have helped me in t the past. Here's what's

Customer Question

Gary you have helped me in t the past. Here's what's happening now. Low Idle/Rough Idle. Low on power. Idle low in park 400 - 600rpm, slight hesitation/surge intermittently. Under load/In gear same low idle, intermittent hesitation/surge when at stop lights,
stalls at times when in gear and stopped or added load (ie...AC or just turning wheel engaging power steering). Here is what has been replaced: Fuel Pump Fuel Pump Relay Fuel Filter Throttle body Gasket Ignition Control Module Ignition Coil MAP Sensor IAC
Valve Coolant Temp Sensor Cap, rotor, plugs and wires replaced in last 6 Months. Motor (New GM motor) was replaced along with new distributor 31 Months ago has 56347 miles on it. Been running great unitl recently. Has never been over heated. All maintenance
has been regular as needed. Don't know what else could be causing issue. HELP?!?!
Submitted: 2 years ago.
Category: Chevy
Expert:  BOBBYSS replied 2 years ago.
Hello, my name is***** you for the question. Can you tell me if the vehicle is running fine at higher speeds?
Customer: replied 2 years ago.
Hello Bobby...you have helped me in the past as well. There is a decrease in power in getting to higher speeds as well as it not feeling as smooth as it use to when at higher speeds. There is no hesitation at higher speeds (No rpm needle jumping or anything). There seems to be no vacuum leaks from anywhere after inspecting all lines around throttle body from what i can see or hear.
Expert:  BOBBYSS replied 2 years ago.
Thank you for the response. From what you are explaining it sounds like you may have a failing MAP sensor or an EGR valve that is not closing properly. Both of these will cause this. I would let the engine idle and tap on the MAP sensor with the handle of a screw driver. See if the idle fluctuates at all when you do. If it does then replace the sensor. I would also check the port to see if it is clogged. If not then see if the EGR valve is holding open. With the engine idling grab the EGR valve and feel underneath it. You will feel a rubber diaphragm in the opening in the bottom. Press on it and see if the idle changes much. If it does not then replace the EGR valve.
Customer: replied 2 years ago.
The MAP sensor is new. Did your tap test no idle fluctuation. Also just went ahead and replaced EGR (it was over 5yrs old and probably had 80k + miles). All that done still no change. Now...just came in from doing more investigating I found when I remove PCV idle RPM improves and hesitation/surge goes away. No stalling when in gear and under load. PCV is due to be changed has around 60k miles on it. Will pick one up in the morning. What are your thoughts?? I'm no mechanic but logic is telling me with PCV removed proper vacuum is acquired. If having new PCV installed still produces same issue are we looking at problem being in throttle body?
Expert:  BOBBYSS replied 2 years ago.
Did you remove and plug the PCV or let it suck in air?
Customer: replied 2 years ago.
Removed PCV from valve from rocker cover left that open....popped vacuum line off of PCV left line open to throttle body sucking air freely. I did plug line to throttle body just out of curiosity and symptom returned then it stalled.
Expert:  BOBBYSS replied 2 years ago.
Thank you. So it actually runs better when there is a vacuum leak?
Expert:  BOBBYSS replied 2 years ago.
Thank you. So it actually runs better when there is a vacuum leak?
Expert:  BOBBYSS replied 2 years ago.
Thank you. So it actually runs better when there is a vacuum leak?
Customer: replied 2 years ago.
Yes...in this instance when "vacuum leak" occurs from PCV being removed from equation...idle is somewhat rough but there is no hesitation like before no needle jumping and no stalling when under load. So based on the information what do you think?
Expert:  BOBBYSS replied 2 years ago.
If the engine runs better when this vacuum leak is created then you may have a valve timing issue or even a clog in the exhaust. Do you have a vacuum gauge? If so please test the vacuum at idle and then hold it at 2500 rpm and hold it there and tell me what it does/
Customer: replied 2 years ago.
No....no vacuum gauge. If i had gauge how would I go about doing test? What result should I get?
Expert:  BOBBYSS replied 2 years ago.
You need to place it on a vacuum port such as the PCV hose. You should get about 15-20 inches of vacuum at idle and it should go up ant hold at the higher rpm and should not fluctuate at either speed.
Customer: replied 2 years ago.
OK...sounds easy enough. When I go get new PCV I will get a gauge and let you know. I know the timing now is about .5 of a degree advanced. Also I currently have about a 3yr old not the best quality aftermarket 3 piece CAT on it now that will be replaced this coming week with a magnaflow direct fit CAT along with new O2 sensor. Been meaning to replace CAT anyway regardless if it has any bearing on current issue have emissions inspection coming due in a couple of months. Would be nice to have this resolved before then.
Expert:  BOBBYSS replied 2 years ago.
The vacuum test will help us to know if there is an exhaust issue also.
Customer: replied 2 years ago.
OK...used vacuum gauge from shop down the road. At idle it read 22 and at 2500 rpm went it up to 24 with no fluctuations at both. One more thing I noticed running at 50 to 70mph feels a little rough. Also replaced PCV with OEM PCV and problem still there.
Expert:  BOBBYSS replied 2 years ago.
With the engine at idle, if you look at the spray pattern coming from the fuel injectors does the fuel look nice and atomized or does the fuel look like it is dripping out or puddling?
Customer: replied 2 years ago.
I will have to take at look at that......did those vacuum readings check out?
Expert:  BOBBYSS replied 2 years ago.
Yes, those look fine.