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Hey guys...having trouble diagnosing an engine stutter that only happens at low RPM.
Here is what I KNOW:
Active codes: P0102 - MAF sensor circuit low input
Stutter only happens when throttle is pushed lightly from a dead stop, or in 3rd gear accelerating slowly from 45-55ish.
Add Sea Foam, stutter goes away completely until that tank of gas is used up, comes right back.
What I've done:
Sea Foam Intake clean
Sea Foam 50/50 injector clean
Checked all plugs and wires. Plugs are fairly clean, newish wires (although they are duralast and only 7mm wires).
Checked all my vacuum lines with starter fluid. Small leak at break booster hose (Vinci power products vacuum booster had been installed, spliced into brake boost hose, no hose clamps used. Removed Vinci box and hose clamped brake booster hose, vacuum leak fixed).
Before I go spend $180 on a new MAF sensor, I was wondering if there were any other likely culprits that I could check first. I know vacuum leaks can cause the P0102 code, but i don't seem to have any. Plugs and wires are good. Maybe clogged fuel filter?
It seems the previous owner was more interested in driving a corvette than owning one, as I have fixed so many small things that were either ignored or half measures taken. Bad Thermostat? Ya, lets just drill a hole instead through it rather than replace a $25 part 🙄
Normally when a DTC says “circuit low” or “circuit high” I’ll look at wiring issues first…your DTC is circuit low “frequency” so you can see if the TB is clean (can set a P0102) and if not go and clean it…if you have a DVOM and know how to use it I will give you assistance in checking the MAF wiring if you need it..if your DVOM has a frequency setting that’s even better…the MAF may also just need a cleaning !!
I will check the throttle body and try cleaning the MAF.
I assumed the sea foam would clean the throttle body as well since the instructions said to position the sprayer 1/4" from the throttle body plate...but now that I think about it, all the sea foam would have completely bypassed the throttle body.
Unless I clear the code in the DIC, it takes 40 ignition cycles to clear a P0102. So should I clear the code after cleaning both and see if it come right back?
I will check the throttle body and try cleaning the MAF.
I assumed the sea foam would clean the throttle body as well since the instructions said to position the sprayer 1/4" from the throttle body plate...but now that I think about it, all the sea foam would have completely bypassed the throttle body.
Unless I clear the code in the DIC, it takes 40 ignition cycles to clear a P0102. So should I clear the code after cleaning both and see if it come right back?
Yes, you can do the cleaning, clear the codes and then run the car and see if the DTC sets again before turning off the ignition…if it returns it will appear as a current or “C” after the P0102…if it comes back you will need to check some wiring before condemning the MAF.
Had the same issue and did the MAF cleaning with CRC and no more issues. I add this procedure to my annual tune up every spring. Also, I use the CRC MAF cleaner annually in my ignition to clean any stuff that found its way in.
Apparently there is no MAF cleaner anywhere in SW Florida right now. Orielly's told me they have been out for 2 months and have no idea when it will be back in stock. Thanks Covid.
So i got 90% rubbing alcohol in a spray bottle and cleaned the best I could. It was very dirty. Used a q-tip on the housing and only sprayed the sensor. Cleaned the throttle body...it was not very dirty at all. Took the entire air box apart, cleaned every bit of it. Changed the air filter, put it all back together.
Cleared the code, came back as soon as I started the car.
Stutter remains. Throttle response and fuel milage have both improved.
I've used non chlorinated Brake Kleen on MAF sensors many times with no ill effects...where in SW Florida are you located ??...if you want to bring the car by I'd be happy to look at it for you. If you have a DVOM this is what you should see with the MAF connector unplugged and then plugged in... you will "back probe" the connector when it's plugged in...you can use a thin needle and guide it along side of the wire from the back. MAF unplugged probing pink wire key on...battery voltage MAF unplugged probing the yellow signal wire with key ON...seeing your 5 volt ref. MAF unplugged probing the black/white ground wire...should be less than 100mv (less than .1 volt) MAF connector plugged in probing the yellow signal wire key ON MAF connector plugged in probing the yellow signal wire at idle. If you rev engine yellow signal wire voltage will decrease as RPM increases. MAF connector plugged in probing yellow signal wire at idle with a frequency setting if you have one in your DVOM.
I HAD a really nice multimeter until I let someone borrow it and they fried it. Probably something I should invest in. Just haven't needed it...until now 😂
I’m right across the river so if you want to bring it by this afternoon or the weekend I can take a look. Always a good idea to put your location in your profile !!
Hello All !!
OP stopped by this afternoon and the only current DTC was P0102…unplugged the MAF connector and power, ground, and 5 volt ref. were OK…plugged connector back in and hooked up the scan tool…MAF grams/second at 2.46 (should be roughly the liter displacement of the engine (about 6.0 to 6.5 grams/second…observed the MAF frequency and at a big fat 0 !!…should be around 3000 Hz at idle…also verified with graphing multimeter and reading the same…verified BAD MAF !!…OP said OEM MAF is on a 2 month back order…OP decided to go with an aftermarket with a good warranty…he said the code cleared and the car runs great but he still sees a slight hesitation at 40-50 MPH when accelerating slowly…OP will be swinging by tomorrow so we will have the scan tool or scope hooked up and go for a ride to see what we can see…maybe TPS signal dropping out or maybe fuel delivery issue…will look at fuel trims…I did a quick relative compression test as I always like to do (plugs are not removed and no compression gauge used but just the starter current is observed while cranking to interpret a compression) and one cylinder was at 85%…all other cylinders were at 100%…looks like if the highest compared to the lowest is within 70% so it should be OK !!
I've been under the weather a bit all week...thankfully not Covid. But because of where I work I had to take precautions regardless.
Changing the MAF sensor made a world of difference in how the car runs. Per C5Diag's advice, I also ran a bottle of techron through and switched to ethanol free premium (available at Walmart Gas Stations and Murphy's). The FlowMaster exhaust which used to be a bit unbearable to listen to during regular driving has quieted down quite a bit during normal driving. The engine idles smoother and throttle response is spot on.
The MAF that was on my car was obviously a very cheap replacement. The body was made of plastic and it did not have a screen on the front. Very happy with the replacement both in fit and finish, and function. The casing is polished aluminum and looks very nice.
A couple odd things happened on my test drive after changing the MAF. First, the code cleared immediately. I say this is odd because I read in a GM Tech Bulletin that it takes 40 ignition cycles with good readings from the MAF to clear a P0120 code.
The second was that several times at full throttle (about 70-80mph), the rpm's suddenly nose dived and came right back up immediately. This happened twice on that drive, but it didn't throw a code. Ot has only happened once since, however I typically do not drive the car hard.
On the third startup after changing the MAF sensor, I got another code. P0410. This has to do with the AIR pump emissions system. However since the AIR pump only runs for the first 2 minutes after startup, it does not affect how the car runs if it is cleared after the 2 minute period. However, the car runs extremely rich during that period.
Since changing the MAF sensor, running techron through the tank, and switching to ethanol free, the stutter has ALMOST completely gone away.
I do intend on getting back with C5Diag once I feel completely well again for further diagnosis! Not only was it great to have the help figuring out what was going on, but it was fun just hanging out with another corvette guy! My wife will never get it...but oh well!
Jeremiah,
Hope you're feeling better !!!...If you're feeling better next week on your days off swing by if you like and I'll take a look. I cleared the P0102 with the scan tool...if I didn't clear it using the scan tool the MIL will go out after the 3rd trip that the PCM didn't see any problems...it will however delete from "history" after those 40 warm up cycles. If the P0410 is still current we can test it using the scan tool bi directionally and we can address that RPM issue too if it's still happening...did you have a loss of power when the RPM decreased or the RPM itself took a nose dive ??
My days off are different this week....thursday and Friday. If you are available either of those days, shoot me a text!
Yes, when the RPMS nosedive, there is a loss of power. About a second each time it has happened. But it hasn't happened recently.
To be honest I am not really too concerned with the AIR system. I plan on putting a LS6 intake with 102mm throttle body, and the vararam ram air cold air intake. Once I do that, it will have to be dyno tuned anyways. I was thinking about maybe just deleting the whole system then. Not sure what the benefits might be??
I would like to figure out which cylinder is running the lower compression though, and see if we can figure out exactly what is going on with this stutter. I'll have to take you on a drive so you can see for yourself. Its pretty subtle now, but still noticable!
Shoot me a text if either of those days work for you!
Thursday is fine…I’ll just do a quick relative compression test with a sync and find out exactly which cylinder it is…ok, we can just go for a ride and record the scan data as see what’s happening…I received my new scope earlier this week so we can use that instead of the scan tool !!
Engine Stuttering
