Can high humidity affect idle quality? '96 coupe

It seems like I have idle issues when the humidity is high. I have noticed this several times now. When it is high I get this lope issue at idle after the car has run for about 15 minutes. Here in NC the air is really dry at the moment. I drove 80 miles yesterday and the car idled very good with no lope. This isn't the first time I have noticed it gone when the air is very dry. Thoughts?

Car has new plug wires, plugs. IAC, TPS, ICM, coil, EGR Valve, vacuum control solenoid, Fuel filter, fuel pump, New injectors, New cap & rotor (they are about a year old now) water temp sensor, air filter, I have used 2 cans of starting fluid looking for vacuum leaks. I do have one code but it is from a post cat O2 sensor that isn't connected up. The lope was there before I changed to high flow cats. I need to get a bung welded in for it.

 

Suggest setting the base idle to 525 when the engine is at operating temp.

You did mention that the problem existed before changing the cats however:

With a CEL on your probably running in open loop & the fuel mixture is to rich when the engine is hot.

A note about the post cat 02 sensor: because of exhaust mods if you still get a post cat code after you reinstall it you can change the depth of the 02 probe. Purchase a pair of 18mm spark plug anti foulers. Drill out the base of one with a 1/2" drill & install it on the 02 sensor then screw the second one with the small hole on & install the assembly on the vehicle. On one vehicle I had without cats I had to use a 3rd anti fouler & space the probe out even farther.

 

I have auto X-ray 6000 and it says it's in closed loop.

I don't expect a code after the O2 is back in but thanks for the tip.

Is it possible there is a problem with the MAF sensor that may be causing this lope?

Also, the voltage on the TPS is on the high side .63. Can I enlarge the adjustment slots to get it more in the mid range recommended?

 

MAF handles humidity quite well - if all is better with the MAF disconnected, it's usually the MAF. Before you do that, check measured air flow with your scanner or better yet, post all of the scan data when the problem is present.

 

I'll be back home later today. I'll get the data then. It's supposed to rain a little later so weather is perfect for it to start that lope again.

 

Ok, I got home ok and still no lope but here is the data from a capture and also operationl data. This was after a 80 mile trip. I didn't cut the engine off before taking these readings.

Capture at idle in Drive

Readness Monitors
Complete Yes
Fuel System 1 Closed Loop
Fuel System 2 Closed Loop
Load Value 1.9%
coolant temp 201
short term fuel trim 1 1.5%
Long term fuel trim 1 1.5%
Short term fuel trim 2 0.0%
Long term fuel trim 2 2.3%
Map sensor 10 in.hg
Engine rpm 586
vehicle speed 0 mph
ignition timing adv. -24.0 (The - is the way the Auto X-Ray reads it I was told. It's actually a +)
Intake air temp 71
Air flow rate 0.73 1lb/min
Throttle position 0%
2nd air status atmosphere /off
Oxygen sensor 1 bank 1 0.105V
Short term fuel trim -1%
Oxygen senssor 2 Bank 1 0.065% V

Operational Data at idle in Drive

fuel system 1 closed loop
fuel system 2 closed loop
load value 1.9%
coolant temp 201
short term fuel trim 1 0.0%
long term fuel trim 1 1.5%
Short term fuel trim 2 0.7%
long term fuel trim 2.3%
MAP sensor 10 in.hg
Engine RPM 579
Vehicle speed 0 MPH
ignition timing -24.0
Intake air 66 F
Air flow Rate 0.73 lb/min
throttle position 0%
Oxygen sensor 1 bank 1 0.795 v
Short term Fuel Trim 1 0%
Oxygen Sensor 2 Bank 1 0.610v
short term fuel trim 2 not supported
Oxygen sensor 1 Bank2 0.115v
short term fuel trim -2%
Oxygen sensor 2 bank2 0.445v
short term fuel trim not supported
OBD II Require (CARB)
battery voltage 13.7
throttle position sensor 0.62 volts
front 02 sensor 0.137V
rear 02 sensor 0.580V
throttle position 0%
Start up coolant temp 35 F
canister purge stolen 0%
EGR duty cycle 0%
IAC 0 steps
Fuel Trim Cell 16
Desired idle 550 RPM
Baro pressure 29.9 "Hg
A/F Ratio 14.7
Engine run time 6784 Sec
Catalytic Converter Temp 1063 F
EGR test count 13
Total misfires 18 counts
Misfire History ( I was supprised to see the misfires on the clys noted. This was not this way before I changed the ICM. It was changed at the same time I put the Cats on. Could the post 02 not being there cause these misfires to happen? The car runs really well, it's hard to believe that many cylinders are miss fireing.)

CYL 1 290
CYL 2 221
CYL 3 7
CYL 4 2
CYL 5 38
CYL 6 34
CYL 7 22
CYL 8 0

Long Term Fuel Trim 131
Rich/Ln Ln/Rich Ratio 1
Knock Retard 0.00
Knock Counts 17471
Block Learn Decel 0
Block Learn Idle 0
Block Learn Cruise 0
Block Learn Accel 0

 

Scan data is normal so you really need to capture when the problem is occurring. History however suggests a general misfire - did it ever pop a 300? That's often dirty injectors - GM has a Bulletin; special warranty 200,000 mile for CA cars only.

 

No 300. As I stated in my first post, injectors are new. Just a few months old.

It's really strange this lope has just kind of vanished for the moment. It's done it before though.

 

Maybe the misfires occurred before the injector swap? It's making a small correction for a Lean Condition, which if you hadn't swapped out the injectors, I'd suspect that they were plugged up. Did you replace with OEM injectors or ones with same rating? You might make sure the gas cap is on securely and that the air filter is clean. Then when you scan while the problem is occurring, note whether the idle is increasing above actual (a surge), or decreasing (symptomatic of a miss) and then see what the Long and Short Range Trims do.

 

I have cleared the scanner and the ECM many times since the injector swap by disconnecting the battery for numerous projects. Here are the injectors my tuner recommended I use in place of the multitechs's. I also ran a set of Bosch III for a while and it was still there with them. It is definitely a lope not a miss.
http://www.fuelinjectorconnection.co...od&productId=4

The PCM has a performance tune. Could that be the cause of the lean condition? This all really started about the time I had the tune done. I wish I had his work sheet but I don't.

I'll get another scan if it acts up again. Thanks for all of your help Suncr.













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I had a very similar problem on my 89.

As a start, I would check the IAC and injector connections to make sure they are fully seated and the weather pack seals are not breached. If the seals have dried out or are damaged, high humidity conditions can result in water vapor getting inside the connector body which results in a high resistance connection.

I had a seal problem with the large bulkhead connector on the firewall below the brake booster. The car would get completely stupid every time it rained. Unfortunately, I didn't find out for sure until water ran into it in a downpour and fried the electrical system. Yet another reason to support only driving the Vette on perfect days ...

HTH

 

Thanks! It's really odd that it didn't do it yesterday. It was damp as hell here. I'll keep chasing it though. Now I have to find the reason behind all those missfires. It'll be my luck the lope will return then.....

 

Another thought ...... is it possible that water vapor is getting trapped in the opti? I seem to remember that this was a problem with the early LT's and GM had to add a vent. That could definitely cause the symptoms you describe.

 

Well, I guess it could be but mine is a '96 and supposed to be vented.

It's still damp here and it started again this morning. Maybe I can get a scan a little later on today to see if anything has changed. The car is not in a garage but in a carport. I guess moisture could be getting in it anywhere.