My Blazer won't accelearte past 25-30 mph......it builds up speed SLOWLY until the speed of 25 mph.....is it possible my air intake valve or exhaust system could be clogged? It is a 1991 S-10 4-door Blazer, Thanks.. THANKS FOR ANY ADVICE Ivan

Extracted from Engine-Codes.com

Code P0507

Possible causes

- Dirty throttle body

- Electric throttle control actuator misadjusted or damaged

- Faulty Electric throttle control actuator

- Intake air leak

- Poor electrical connection to the Intake Air Control (IAC) valve


What does this mean?

Tech notes

If there are no intake leaks, clean throttle body, adjust engine idle and erase engine code. If the code comes back you may have to replaced the Electric Throttle Control Actuator (Motor) to repair the problem.



There is a factory service bulletin for the following Chevrolet models:



2006-2008 Chevrolet Trail Blazer

2007-2008 Chevrolet Avalanche

2007-2008 Chevrolet Express

2007-2008 Chevrolet Silverado

2007-2008 Chevrolet Suburban

2007-2008 Chevrolet Tahoe

Chevrolet Factory Service Bulletin OBDII Code P0507


What does this mean?

When is the code detected?

Thi P0507 code sets when the Powertrain Control Module (PCM) detects an engine speed outside of the Idle Air Control (IAC) valve range of control.

Possible symptoms

- Engine Light ON (or Service Engine Soon Warning Light)

- Engine hard to start

- Rough or erratic idle speed

P0507 Chevrolet Description

The Idle Air Control (IAC) valve is a Powertrain Control Module (PCM) controlled stepper motor located on the throttle body. The stepper motor drives a valve pintle which protrudes into a passage that bypasses the throttle plates. The PCM commands the IAC valve pintle to extend to decrease the idle speed. The bypass air flow is reduced and the idle speed decreases as the pintle approaches its seat. The PCM retracts the IAC valve pintle away from its seat to increase the idle speed. The retracting of the IAC valve pintle allows more air to bypass the throttle plates. One of the PCMs uses for the IAC system is to maintain a desired idle speed. This DTC sets when the PCM detects an engine speed outside of the IAC\'s range of control.





Read more: http://engine-codes.com/p0507_chevrolet.html#ixzz3ObdI2chF

If it's backfiring through the intake, then more than likely it's a timing issue. The distributor cap has the cylinder numbers molded into it where the plug wires go... Make sure the wires are in the right spots. If that's good, then it's possible the distributor isn't lined up right.

I’m happy to help further over the phone at https://www.6ya.com/expert/jason_00b31cc8f593773a

Could be a faulty idle air control valve, or a dirty throttle body.
The computer controls idle speed by regulating the amount of air entering the intake thru the valve.

An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The cars computer or PCM (powertrain control module) receives information from various sensors and will output signals to adjust the idle air control motor in or out to adjust engine idle speed by controlling engine idle air. An idle air control motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the idle air control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak idle air control motor.

In most cases problems with idle speed involve the idle air control valve or a dirty throttle body. The computer controls idle speed by how much air is allowed into the intake thru the control valve.
If the throttle is not sticking, I would check the valve and the bore of the throttle body.
You could also have a vac leak but that would usually be a constant problem.

This engine has automatic idle speed control, the computer controls a "air bypass" valve on the side of the throttle body where the air intake hose from the air cleaner is connected, the valve and the throttle butterfly get "sludged" up and this causes all kinds of idle problems and off idle stall, see full list below and fix for the problems

Here is the common cause of surges, cold stalls, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours.

To correct this problem Buy a can of throttle valve cleaner (it is made by CRC) from the local auto parts store, NEVER USE CARB CLEANING SPRAY, IT DESTROYS THE ANTI-STICK TEFLON COATING, spray it into the air intake through the throttle body of the engine until you have used about half the can, you will need to hold the idle up while you do this, it will try to stall, after this shut the engine down and disconnect the Negative (-) battery cable for 5 minutes. The intake is now clean, if you continue to have the idle speed control problems you may need to seek the help of a professional.

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.----------

Getting this possibilities checked will help.Thanks.Helpmech.

You may have a partially plugged fuel filter or a weak fuel pump causing your problems. When you slowly build up speed to, say, 65 mph, it doesn't take a lot of fuel all at once to get to that speed but if you try to accelerate more quickly to that same speed you essentially run out of fuel which will cause the engine to bog...which then causes the transmission to downshift one or more gears...which then will allow the engine to speed up considerably but you won't really gain all that much speed. Same goes for passing someone: If you ease into it you will be using the fuel that's available more efficiently but if you step on it then you have way more air than fuel entering the engine and it just won't hardly go much faster until the fuel supply catches back up again. The quickest way to figure out what is happening is to have someone test the actual fuel pressure during a test drive to see if the pressure remains normal or falls off as the problem occurs. If the fuel pressure does fall then I always change the fuel filter first and test it again. If the pressure is normal and the problem is gone then you've found the culprit. If the pressure is still low then you most likely have a weak fuel pump. A restricted catalytic converter can also cause similar problems but is much more rare. Good luck, hope this helps!

First thing to do would be a tune up with plugs and wires, also the fuel filter. If the motor is trying to accelerate faster than the car is moving I would check Transmission fluid. Hope these ideas help to get you in the right direction. Have a good day.

I would start by cleaning the inside of the Mass Air Flow sensor, dirt gets on the sensor element from the air going through and causes these kinds of problems, a company called CRC makes the spray cleaner for MAF's, any good auto parts store will have it, the MAF is located in the air intake hose to the engine. Another thing to check is the throttle valve and air bypass idle speed control valve for sludge, use the following procedure I have written to perform this.
Here is the most common cause of surges and stalls and low idle, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.