90 chevy 1500 idles rough and bogs when accelerate???

**ShortBed350** · 05-10-2011, 11:36 PM

Hello, i have been having a problem with my truck for a couple weeks now when i go to start it it will die if i do not give it gas then when it warms up a little it will idle high then real low also when i got to accelerate from a stop it will bog down?I discovered a loud sucking noise from IAC valve could it be that? I have replaced fuel pump,fuel filter, spark plugs and wires,Throttle Body gasket,o2 sensor,MAP sensor,knock sensor,coolant temp sensor. And i have cleaned throtle body numeroues times.But about a week or so before the problem i had installed a K&N filter and got rid of all the old housing and also put fuel injector cleaner in it could this have messed up something? Please help I want my truck back=/ anything is better then nothing. Thanks

**98BlueZ71** · 05-11-2011, 01:32 AM

yeah clean the IAC valve

**helo** · 05-11-2011, 07:31 PM

bad sensor ground or cts wiring? Try back-probing the CTS pin on the ECU connector with a multimeter and see if the measurement is out-of-spec (just compare to a direct measurement of the sensor prongs themselves).

7747 pinouts <- see pic #1

**ShortBed350** · 06-01-2011, 01:22 AM

Okay I replaced IAC Valve that diddnt really seem to do anything except for the sucking noise is not as loud I check alot of the wiring and it all look pretty good any other suggestions?

**Srabai47** · 06-11-2011, 11:19 PM

loosen the distributor clamp, and slowly twist the distributor to the right. just slightly. i know it sounds scary but to be safe, mark where the distributor aligns with the block before you loosen it. if it makes it worse, twist it the other way. do all this while the engine is running. also to reach the distributor clamp bolt you'll need to remove the air cleaner assembly to reach the 15mm bolt.

**helo** · 06-12-2011, 03:39 PM

Elaborate on 'checked the wiring and it all looks pretty good'

If you didn't pull every ground connection apart and sand everything until shiny, start with that. A bad sensor ground will make the CTS reading artificially low, causing the ECM to DUMP fuel on a massive scale (your bog, bad idle, etc..).

Bad vacuum hose(s) could be to blame, as well. Especially the hose that runs to the MAP sensor..

**ShortBed350** · 09-27-2011, 10:49 PM

Okay I have not been on in awhile but i have replaced the IAC valve that did nothing for me I've checked the wiring to some of the sensors and found that almost all of them were reading as to what they are suppose to be at except the wiring going to the sensor to the side and kinda underneath the MAP (im not sure what sensor it is) so i started folllowing the wiring and i found some cuts in it so i put a ground to that wire and tried it again and then it worked so i just kept the temporary ground on plugged it back in reset it then tried it no luck... now how do i find out why its not grounding out? do i continue to follow?? Also I've had people say that its my TPS sensor so i went to do the test for that it said when throttle closed it should be at .60 mine was at .59 and wide open throttle should be at 4.5 mine was at 4.30. Even though it's just a little bit lower is it bad? And finally when i was goiing through some of the wiring i found a purple wire (right around the distributor cap) the end looked just like to the o2 sensor and its also a purple wire any clue what that goes to i couldnt seem to find anything?? Also any other suggestions as to what might help fix my truck i'd appreciate it

**91vortec** · 09-28-2011, 09:53 PM

was the wire plugged in to anything? or just hanging there

**ShortBed350** · 09-29-2011, 07:55 PM

It was plugged into the wiring harness.

**ShortBed350** · 10-03-2011, 11:26 PM

I replaced the TPS today and no luck any more suggestions?

**Eagle-Mark** · 10-04-2011, 01:37 PM

Check fuel pressure.

Set timing correctly.

PVC valve.

Check for error codes.

Plug in a scanner to see data.

Kingman? AZ? You should have no corroded ground issues unless the wiring has been messed with by human hands.

Is the motor stock? How many miles on it? Burning oil?

**ShortBed350** · 10-11-2011, 11:31 PM

I Finally got her i replaced the fuel injectors and the fuel pressure regulator and she runs like a dream Thanks for all the help guys

**tib_nordstrom** · 10-25-2011, 11:12 PM

I just went threw the same my brothers 90 chevy did the same but his was a bad distributor but my 92 did like urs is doing and if I was u seeing how u have replaced the iac valve and tps replace the map sensore and see if that does it. Mine would idle rough and my check engine light came on and going 50 mph I could drop it in 2nd and it sound like it was baggin out. I replaced the oxygen sensor and the map snesor and my gmc came back alive ;)