Tip & How-To about Mercedes-Benz E-Class

Air intake by engines - faults

1b) Air : leaks in air intake
Leaks in the air system can occur both before and after the throttle plate. In both cases the additional air entering is not measured by the air mass meter and causes the engine run unevenly. Engines with motor-driven idle control of the throttle plate may be able to accommodate minor air duct leaks. Hot engine restarts can be problematic if the air being drawn in is from the immediate surroundings of a very hot engine.All air ducting should be free of any leaks due to cracks or improperly fitted junctions.
Leaks after the throttle plate and into the inlet manifold severely compromise the ECU's ability to match the amount of injected fuel to the amount of 'measured' air supplied to the engine during 'closed cycle'.Although the ECU does its best to adapt and accommodate the change in air intake the engine remains rough and is less responsive to demand and often the Check engine light will become lit and codes such as P0171 (lean fuel mix) will be set. All vacuum lines should be thoroughly inspected for cracks, splits and loose fitting joints. This entails twisting the pipes to get an all-round look and feeling along the length of every less visible vacuum pipe. Many leaks can be isolated by disconnecting the vacuum lines in turn and temporarily plugging up both the attachment points and the tube ends and then monitoring the effect; a purge valve jammed open or a crack in the tubing on the EVAP system is very hard to detect other than by using this approach. Other points that may avoid easy leak detection, such as the junction between intake manifold and the cylinder head or around the injector body seals, can be tested by methodically spraying the suspect area with a fuel source (cigarette lighter fuel, alcohol, carburetor choke cleaner, propane gas, WD40 etc). A temporary surge in engine revs or perhaps stall, in response to the spray being sucked in and ignited, will confirm a suspected leak.
Engine characteristics in response to an air leak mimic the effects brought about by a faulty throttle position sensor or idle air control valve.All are related to the ECU being unable to maintain a normal ratio between the fuel dispensed and air available.
Possible leaks before the throttle plate:

  • · Air ducting connections
  • · Positive crankcase ventilation valve/crank case breather pipe/cam cover vent
  • · EVAP Fuel vapor evaporation control system that exits at the throttle body either at, or close to, the throttle plate

Possible leaks in the inlet manifold (after the throttle plate):
  • · Fuel pressure regulator valve
  • · Auto transmission in-gear hold
  • · Brake servo pipe
  • · Manifold absolute pressure sensor connection
  • · Exhaust gas recirculation valve
  • Ancillary vacuum line controlled systems
NEXT 2) Fuel systems

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Inermittently when coming to a stop the car accelerated like wide open throttle with foot on the brake.


Is the check engine light on , or any other lights ?

Chart 5

  • Unique Idle Concerns:
    • Fast Idle
  • Additional Drivability Concerns:
    • Diesels/Runs On
Note: If vehicle runs normally after the ignition key is turned OFF, check for damaged ignition switch, IGN RUN circuit short to power, VPWR circuit short to power, etc. Refer to applicable Wiring Diagram and/or Workshop Manual.
SYSTEM/COMPONENT REFERENCE (Section 5 Pinpoint Test unless noted)
  • Base engine air leaks, including proper sealing of intake manifold and components/vacuum lines attached to intake air (such as the PCV, EGR or IAC valve/vacuum lines).
  • Visual, Engine System - General Information Section 303 of the Workshop Manual.
  • Verify engine operates at normal temperature.
  • Visual (refer to Symptom Index, or Engine Cooling Section 303 of Workshop Manual, to diagnose any cooling system concerns that are present).
  • Fast idle concerns:
  • Key on, engine off, monitor TP MODE PID while wiggling TP sensor circuits. TP MODE PID can also be monitored during vehicle drive. With throttle closed, TP MODE PID must be C/T (closed throttle).
  • TP Mode PID is not C/T with throttle closed: NOTE: At vehicle start, the TPREL will begin at about 1.25 volts, and count down to the lowest TP V value seen since engine start. If the TP V value goes below the "normal" range, then increases again, TPREL will set to the lower voltage. If TP V is about 0.04 volts greater than the TPREL value at closed throttle, the PCM will go into part throttle mode.
  • Monitor TP V and TPREL PIDs for sudden changes while checking for intermittent TP circuit/connector concerns. Also check for loose/worn throttle plates. If no concern is found, GO to Z1 in Section 5.
  • Intake Air System (air leaks)
  • GO to HU1
  • Idle Air Control (IAC) System
  • GO to KE1
  • Additional Testing
  • GO to Z1
Do you know what these thing's are that I have listed above ? Mostly the TP - throttle position sensor . These are known to cause this type of problem . Has it ever been changed before ?

Oct 27, 2015 | 2003 Ford Thunderbird

1 Answer

my chrysler pacifica hesitates at 40 mph and it wont go any faster what could it be


Is your engine management light on (mil) test it with obd scanner for code if light is on. If not you might have an air or a vacuum leak. This is very common! Open the hood and listen for a hissing sound when the engine is running. Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow. If it is hard to pinpoint take some brake cleaner or starting fluid around the intake manifold and vacuum lines and see if the engine stumbles or if the idle is affected. Be extremely careful when doing this!

Also, your throttle body may be carboned up and need to be cleaned! This can cause all sorts of idle and hesitation problems. This is caused by the throttle plate not seating properly. The First thing i would do is clean out the throttle body with some throttle plate and intake cleaner and a small brush.

Another common cause would be the Idle Air Control motor. This is very common on older cars. The IAC motor gets lazy and cant keep up with the fast idle changes. Also when the IAC motor is out, I rec to check the passages for carbon build up. If they are plugged they need to be cleaned out.

Possible Causes
Check for air leaks in the Air Induction system (e.g., in the intake manifold)
Check for air leaks in the PCV system and in its related hoses and/or valve
Idle air inlet passage or throttle bore is dirty or full of deposits
IAC valve has failed
Throttle plate, throttle shaft or linkage is damaged or sticking
TP sensor is out-of-range or "skewed" high

Sep 16, 2012 | 2007 Chrysler 300c AWD Sedan New Cars

1 Answer

1998 buick lesabre stalls at times when stop and start acceleration again.


Hi Alan:
You might have an air or a vacuum leak. This is very common! Open the hood and listen for a hissing sound when the engine is running. Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow.
If it is hard to pinpoint take some brake cleaner or starting fluid around the intake manifold and vacuum lines and see if the engine stumbles or if the idle is affected.

Also, your throttle body may be carboned up and need to be cleaned! This can cause all sorts of idle and hesitation problems. This is caused by the throttle plate not seating properly. The First thing i would do is clean out the throttle body with some throttle plate and intake cleaner and a small brush. Another common cause would be the Idle Air Control motor. This is very common on older cars. The IAC motor gets lazy and cant keep up with the fast idle changes. Also when the IAC motor is out, I rec to check the passages for carbon build up. If they are plugged they need to be cleaned out.

Possible Causes
Check for air leaks in the Air Induction system (e.g., in the intake manifold)
Check for air leaks in the PCV system and in its related hoses and/or valve
Idle air inlet passage or throttle bore is dirty or full of deposits
IAC valve has failed
MAF sensor is dirty, "skewed" or installed improperly
Throttle plate, throttle shaft or linkage is damaged or sticking
TP sensor is out-of-range or "skewed" high

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day and Merry X-mas.

Dec 22, 2011 | 1998 Buick LeSabre

2 Answers

P1193 error code car wants to stall when stopping and accelerating


P1193 = Detected engine speed below 470 RPM. There are several possible causes/components which can contribute to this drivability issue. ELECTRONIC THROTTLE SYSTEM (ETS). In most cases, an ETS related DTC will set in pairs of codes. The first code denotes the related system or component. The second code is for the specific fault detected.
There was also probably P1191 - limp home

For this issue, on frequent occations I've found the throttle position sensor (TPS) (potentiometer) had bad spots in it and subsequently sending erratice signals to the ETS Control Module (additionally, the throttle body and plate had carbon buildup inteferring with the intake air flow. Also check for air leaks (intake air hoses, vacuum lines & tubes for cracks/leaking). Clean the throttle body & plate. Bench test the TPS. You also have an APS (Accelerator Position Sensor) located on the RH side engine compartment near the firwall next to the strut tower. These are the initial components to check/examine. Replace as needed.


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Aug 31, 2011 | 2001 Hyundai XG300

1 Answer

My 99 Park ave will stall at red light. Or sometimes idle will fluxuate from 500 to 2000. Somebody mentioned the air mass filter, another mentioned the throttle celenoid. These are expensive items to guess at. The car runs great with no hesitation on open rd. Only acts up in stop and go traffic.


I would check the fuel pressure regulator. It is located on the fuel rail. It is round, about a quarter size and has a vacuum line going to it. If the regulator is leaking gas than it can cause this problem. Pull off the vacuum line that goes to the regulator. Be absolutely sure there is no gas in the vacuum line. If there is, the diaphragm has ruptured and there is gas entering the engine that is not accounted for and the regulator will need to be replaced!
Also, you might have an air or a vacuum leak. This is very common! Open the hood and listen for a hissing sound when the engine is running.
Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow.
If it is hard to pinpoint take some brake cleaner or starting fluid around the intake manifold and vacuum lines and see if the engine stumbles or if the idle is affected. Be extremely careful when doing this!
Also, your throttle body may be carboned up and need to be cleaned! This can cause all sorts of idle and hesitation problems. This is caused by the throttle plate not seating properly. The First thing i would do is clean out the throttle body with some throttle plate and intake cleaner and a small brush. Another common cause would be the Idle Air Control motor. This is very common on older cars. The IAC motor gets lazy and cant keep up with the fast idle changes. Also when the IAC motor is out, I rec to check the passages for carbon build up. If they are plugged they need to be cleaned out.
Check for the following conditions:
Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage.
Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.
Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.
Vacuum leak. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, faulty or incorrectly installed PCV valve, leaks at intake manifold brake booster hose disconnected, oil filler cap, oil level indicator loose or missing, etc..

The SES light is the Service engine soon light. If you get a chance to have the computer scanned, let me know the codes and I will be able to get you more specific information.

Feb 27, 2011 | Buick Park Avenue Cars & Trucks

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