98 tahoe irregular idle

[Asfalto]

Hi everyone!
this is my first thread here, i'm in italy and here american cars are unknown things..founding this forum makes me hoping to solve my problems!
the car is a 1998 tahoe 5,7 vortec
the problem (very often showing): in D, with the brake pedal pushed, idle is irregular in a continuos revvig between 500/900 rpm; it's annoying at the lights and expecialy when doing some precision move (like park the car in a small space).
thank you for the support!

 

[Phone Man]

Yup had that problem.... surging idle. Clean the MAF sensor first. It measures air flow. Is your check engine light on?

 

[gpracer1]

Check the AIC MOTOR , air idle control.
It may need to be cleaned. This is assuming that everything else is normal and the engine isn't misfiring on a cylinder.

 

[Asfalto]

thank you guys!
the check engine light is off.. but maybe it is burned; should it light on when i turn the dashboard on (and suddenly go off when the engine starts)?
i'm wating for the shop manual to come from the states (it will take 2 weeks), can you tell me where MAF (or MAP) and the AIC MOTOR , air idle control are located?

thanks again!

 

[tahoe.mkIII]

bump

 

[gpracer1]

thank you guys!
the check engine light is off.. but maybe it is burned; should it light on when i turn the dashboard on (and suddenly go off when the engine starts)?
i'm wating for the shop manual to come from the states (it will take 2 weeks), can you tell me where MAF (or MAP) and the AIC MOTOR , air idle control are located?

thanks again!

The MAF is between the air filter box and the throttle body. The AIC is on the throttle body.

 

[Asfalto]

thank you guys!
i'll let you know if the problem goes away.
bye

 

[Asfalto]

I cleaned the MAF with crc maf cleaner but problem persists.
i got the scanner at last, and it reads code p1345: crankshaft position (ckp) - camshaft position (cmp) correlation.
Can it be the cause?
Now I noticed that at cruising speed (like 50 mph), with a very light press on the gas pedal, the engine shakes and it gives no significant power.. I have to add a bit more of pressure to get a real improve of power/speed.

 

[SunlitComet]

uh yeah that is a problem your crank/cam sensor correlation is off and with certain timing and off-ness can cause misfiring.

Can your scanner read live data? specifically CAM_RETARD?

 

[Asfalto]

I bought AutoLink CAN OBDII Code Reader for 50 $ at amazon; it gives a lot of live data and one is SPARK ADV. I don't know if is the same for cam retard.. it reads +20 °.
Anyway I tried to rotate the distributor but that data doesn't change meanwhile the engine started getting worst misfireing so i putted everything back with the previous setting.
problem an code persist!

 

[SunlitComet]

not the same thing. just head to a dealer or local shop who has a good scanner and ask the to set it for you. if not possible let me know i will find a amazon sold scanner that can if you really need.

---------- Post added at 04:28 PM ---------- Previous post was at 04:26 PM ----------

what other live data is displayable?

 

[Phone Man]

He's in Italy Sunlit.
The timing is controlled by the computer. However it does need to be set to "0". Once you get a scanner that can read cam ret, the engine has to be reved up to over 1000rpm and held there. At the same time, turn the distributor until the scanner reads ZERO. plus or minus 1-2 degrees is ok. Then tighten the bolt on the distributor and the timing is set. Good luck and keep us posted.

 

[Asfalto]

not the same thing. just head to a dealer or local shop who has a good scanner and ask the to set it for you. if not possible let me know i will find a amazon sold scanner that can if you really need.

---------- Post added at 04:28 PM ---------- Previous post was at 04:26 PM ----------

what other live data is displayable?

I got this one http://www.amazon.com/Autel-AULAL30...3727184&sr=8-3&keywords=autolink+obd2+scanner it's an amazing machine
, it has 6 pages of live datas..when I'll have a bit of time i'll write them down.

He's in Italy Sunlit.
The timing is controlled by the computer. However it does need to be set to "0". Once you get a scanner that can read cam ret, the engine has to be reved up to over 1000rpm and held there. At the same time, turn the distributor until the scanner reads ZERO. plus or minus 1-2 degrees is ok. Then tighten the bolt on the distributor and the timing is set. Good luck and keep us posted.

I've alredy followed this procedure but without a scanner it's not easy..
however I'll go to my frend shop hoping he has a good scanner.. now he's out for summer holydays.
I'll let you know as soon as I can!
thank you guys, I appreciate very much your hints!!

 

[SunlitComet]

Duh, I know he is in Italy. He can't be the only one there driving a American vehicle that needs service.

you need one that reads gm enhanced stuff. i right now use a pc based system but there is this handheld that should do a lot for you. http://www.amazon.com/AutoXray-AX7000-Diagnostic-Playback-Capability/dp/B001LJIZHO it is new and i have not tried it myself. i am holding on for something more pricey which is also bi-directional. but this one read gm enhanced data stream and while the screen shots in manual did not actually show the cam retard reading it shows some of them. I just image you have to change data pages as there are a lot of readings available. it even claims to be bi-directional which allows you to actuate components for testing. and it is cheap considering that. i am tempted to try it myself now.

---------- Post added at 05:37 AM ---------- Previous post was at 05:23 AM ----------

by the way if you want to shoot from the hip and are still shaking when driving rotate the dizzy in 2-3 degrees at a time in the opposite directions you headed before and drive it again to trigger the misfire. if no more then pull the three fuses under the hood that start with ecm in their description for a few minutes to wipe the code or or wait 3 consecutive trips and it will kill the light on its own if truly fixed. if you disconnect power tho upon first start wait for engine to warm up and then drive about 5-10 miles(10-20 km?) at part throttle and then shut down and let it cool down. repeat once. this constitutes a trip as specified by service manual. truck may act a little strange until performance returns. maybe you will get lucky if you can not get the better scanner.

---------- Post added at 05:47 AM ---------- Previous post was at 05:37 AM ----------

just saw some reviews that the company may not support it tho autoxray claims it is new. so maybe email them. not sure how well the the phone will accept an international call on an 800 service.

---------- Post added at 05:49 AM ---------- Previous post was at 05:47 AM ----------

http://autoxray.com/contact_us.php

---------- Post added at 05:53 AM ---------- Previous post was at 05:49 AM ----------

and verify with them that is does read cam_retard for your year.

 

[chevyt454]

I'm going through the same thing

 

[Asfalto]

Thank you again Sunlit!
keeping you all informed!

 

[Asfalto]

Hi Sunlit, here’s what you ask me about my scanner live data
it is set on metric units

DTC_CNT
FUELSYS1
FUELSYS2
LOAD_PCT (%)
ETC (°c)
SHRTFT1 (%)
LONGFT1 (%)
SHRTFT2 (%)
LONGFT2 (%)
MAF (KPa)
RPM
VSS (Km/h)
SPARKADV (°)
IAT (°c)
MAF (g/s)
TP (%)
O2S2OC B1S12—B2S12—O2B1S1 (V)
SHRTFTB1S1 (%)
O2B1S2 (V)
O2B2S2 (V)
SHRTFTB2S1 (%)
O2B2S2 (V)
OBD SUP

 

[SunlitComet]

Unfortunately that is generic OBD2 data and does not include cam retard. You will have to get a different one or visit a shop with one.

 

[Asfalto]

solved!
the code p1345 was caused by a worn distributor gear.
I have also changed cap&rotor and spark wires (I think they were from year 1998).
now it runs fine, smooth and powerful and the check engine light turned off.

thank you everyone for the assistance.