epokiak Posted July 12, 2015 Share Posted July 12, 2015 I have a 2000 Oldsmobile Alero 3400 that runs rough at idle, surges and would eventually stall. codes p0131 and p0171 for lean condition, replaced the upstream o2 sensor was fine for week, and returned with surges at idle, on the highway and off idle the engine runs fine, replaced the maf sensor, cleaned the iac vlalve, inspected the map sensor vacuum hose, removed the egr valve and plugged the egr port, no change in idle, when the maf sensor is unplugged the idle levels out, smoke tested the engine and cannot see any leaks other than the base of the egr valve and a slight smoke around the shaft of the throttle body, any info would be great.. Thank you Ernest Quote Link to comment Share on other sites More sharing options...
8WA Sman Posted July 13, 2015 Share Posted July 13, 2015 With that style engine where the valve cover splits with the intake,check for a vacuum leak from the crankcase side. If you have or can get some fuel trim reading at idle and at 2500,also mass air flow g/s at hot idle no load. You could check your o2 sensor for being biased at idle by adding some type of enrichment into a vacuum hose. Quote Link to comment Share on other sites More sharing options...
sneakypete Posted July 13, 2015 Share Posted July 13, 2015 still setting codes? do you have a scan tool that you get post the fuel trims. Quote Link to comment Share on other sites More sharing options...
epokiak Posted July 13, 2015 Author Share Posted July 13, 2015 long term fuel trims are at +22%. short term are hovering around 0%. so it can have an air leak from inside the engine? i am fairly new at non ford brands, so taking a bit to learn the diagnosis of the alero, from some research on the internet the 3800 has had some issues. Quote Link to comment Share on other sites More sharing options...
ktmlew Posted July 13, 2015 Share Posted July 13, 2015 long term fuel trims are at +22%. short term are hovering around 0%. so it can have an air leak from inside the engine? i am fairly new at non ford brands, so taking a bit to learn the diagnosis of the alero, from some research on the internet the 3800 has had some issues. Do you happen to here a weird squealing sound occasionally? Remove the oil cap and put your hand over the opening. How much vacuum pull do you feel? If it sucks your hand down, the intake gasket is blown. Quote Link to comment Share on other sites More sharing options...
epokiak Posted July 13, 2015 Author Share Posted July 13, 2015 there is a weird sound from the center of the engine intermittently that would go away, sounds like another engine running inside the engine. Quote Link to comment Share on other sites More sharing options...
8WA Sman Posted July 13, 2015 Share Posted July 13, 2015 Block off the PCV system including the fresh air side and put a sensitive vac gauge in the dipstick tube and see if crankcase has vacuum(should have pressure) Quote Link to comment Share on other sites More sharing options...
ktmlew Posted July 13, 2015 Share Posted July 13, 2015 Block off the PCV system including the fresh air side and put a sensitive vac gauge in the dipstick tube and see if crankcase has vacuum(should have pressure) ^this^ Alos some engines PCV valve have an o-ring around the housing to seal it to the bore. If you don't install the o-ring it will cause issues. If the intake gasket is leaking vacuum into the crankcase the noise you hear is air being sucked past the front or rear main seal. It runs for a couple minutes until the vac gets lower than the seal can hold. Then it "farts". Quote Link to comment Share on other sites More sharing options...
sneakypete Posted July 14, 2015 Share Posted July 14, 2015 since this is a 3.4L the pcv does not have an oring. just installs into the left (front) valve cover. what does your trims do at 2500 rpm. what iac counts at idle. whats the map in kpa at idle. or better yet. what's your vacuum gauge read. assuming you have high trims at idle only, try pinching or blocking the brake booster hose. also, the dirty side of the pcv connects to the top of the intake under a bracket. I've had many tubes deteriorate there. spray some brake clean and watch the o2's and fuel trim. Quote Link to comment Share on other sites More sharing options...
sneakypete Posted July 14, 2015 Share Posted July 14, 2015 circled is the area of where the pcv tube can deteriorate. don't forget to check the clean side of the pcv system at the right (far) valve cover as well. Quote Link to comment Share on other sites More sharing options...
ktmlew Posted July 14, 2015 Share Posted July 14, 2015 circled is the area of where the pcv tube can deteriorate. don't forget to check the clean side of the pcv system at the right (far) valve cover as well. YES! Very common issue on that style. I was thinking of the newer intake. Quote Link to comment Share on other sites More sharing options...
epokiak Posted August 4, 2015 Author Share Posted August 4, 2015 I'm leaning to intake gasket leak, but the customer does not want to spend the labor time to do the gaskets! Quote Link to comment Share on other sites More sharing options...
mchan68 Posted August 5, 2015 Share Posted August 5, 2015 Then pitch it. As I get older, I'm losing my patience with those kinds, who have problems that aren't the easiest to diagnose but don't want to pay to play. Quote Link to comment Share on other sites More sharing options...
lmorris Posted August 5, 2015 Share Posted August 5, 2015 We had one in with similar concern, turned out to be the MAF sensor wires where damaged and a voltage was being induced by the positive cable off the alternator. Just a thought. Quote Link to comment Share on other sites More sharing options...
Aaron Posted August 6, 2015 Share Posted August 6, 2015 Ernest are you still at Kingland? Quote Link to comment Share on other sites More sharing options...
epokiak Posted August 6, 2015 Author Share Posted August 6, 2015 No left Kingland mid March, we opened up a Auto Shop/ towing/ car wash. Ernie's Automotive. Been busy Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.