MAP, boost and lambda sensor faults

Turbo: the boost (MAP) sensor

• One owner investigating turbo stall found the Turbo uses a Bosch pressure sensor, part 0261230042, used by many manufacturers. It cost about £90 in 2013. Cheaper unbranded "compatible" sensors were said to be best avoided.
• The same owner says it isn't really a MAP sensor but a boost pressure sensor, which the ECU uses at the top of the charge cooler to drive the boost control valve that opens when you lift off, to prevent stall. This is his understanding of the system.
• Another owner says any Lotus Europa part number starting X116 is a VX220 Turbo part, and that it can be cheaper to buy a Vauxhall part from Lotus. Check the part number with the supplier before relying on this.
• Getting to the sensor means taking out the offside rear wheel arch liner (one owner's comment, who put it off).
• Genuine only. One owner says cheap pattern MAP sensors cause serious problems and to use only genuine ones. Another had a supercharged car that stuttered and sometimes stalled when the throttle was blipped, and it turned out to be the MAP sensor.
• For a MAF, see MAF sensor faults.

Boost control parts

• The Turbo has two boost solenoids. According to one owner they are near-identical except for the size of the vacuum pipe fixings. The one on the inlet manifold works with the recirculation valve and the vacuum box, and the one on the turbo works with the actuator. One owner says the lower Torx bolt on the rear solenoid is very awkward to reach.
• An owner who replaced a rear boost control valve and a recirculation valve with a Forge copy, and re-clipped vacuum pipes, still had turbo stall and moved on to cleaning the sensor. Nobody reported the outcome.
• Actuators do fail, even the uprated ones (one owner).

Vacuum leaks

One owner says vacuum leaks cause a poor idle and trouble at small throttle angles, because the engine draws unmetered air through the leak rather than through the MAF, and that they give an overall error in short-term and long-term fuel trims. His test: disable as many vacuum hoses and joints as you can, with a T-piece from the inlet manifold direct to the fuel pressure regulator and the recirculation valve, and blank off the vacuum feed to the carbon canister breather on the fuel tank. Then the only leaks left are the brake servo or the recirculation valve itself. He also asked when the coil pack and plugs were last serviced. See Brake servo hose.

Lambda sensor and P0130

A Turbo owner (2014, with a VXR turbo fitted) had hesitation on gentle acceleration. At low revs and light throttle the boost would build to a steady 15 psi, run rough for a few seconds, then drop to 0 psi. It was also very hesitant pulling away from a standstill. A new MAF made no difference, and a code reader then showed P0130 (O2 sensor circuit, bank 1, sensor 1, the front sensor).

• What the live data showed. After a minute or so the sensor reading and then the fuel trims flat-lined until the car was restarted. One owner says that is probably the ECU dropping into open loop and ignoring the sensor, which fits a P0130 and means replace the sensor. Another owner says a flat line would suggest a loom problem. The thread didn't settle which.
• The fix. A new Bosch pre-cat lambda sensor (about £50). It peaked at about 0.7 V instead of 1.1 V and updated more often, it kept working after five minutes, the hesitation and the partial-throttle judder went and power on higher loads improved. After he reset the fuel trims the ECU needed to relearn, and he noticed a slight pull-back on sharp high-load runs in second gear, which he hoped would settle. One owner got the same code and a new front sensor fixed it, with no symptoms other than the warning light.
• What is normal. The front sensor is a narrowband type that works in a narrow range, roughly 14.1 to 15.5 AFR, and is used mainly at idle and very low loads (one owner). It should swing between about 0.2 V and 0.8 V, from slightly rich to slightly lean about once a second, once the engine is fully warm (the sensor only works above about 350°C). One owner quoted the sensor maker as saying that at about 2,000 rpm it should switch in about 300 milliseconds. An OBD reader samples slowly so it can look slower. The bouncing is correct behaviour.
• How the ECU uses it. One owner explains that the fuel is made richer or leaner by steps depending on the lambda reading ("bang-bang" control), and the trims it learns are used in open loop under high load.
• P0130 has several variants. A freeze-frame read helps: high voltage (above 1.5 V), low voltage (below 60 mV), slow response, or the control limit reached lean or rich for 18 seconds (the list from one owner).
• Brand. One owner says prove it is the sensor first, and then buy a Bosch one rather than an unbranded part. Two later replies preferred genuine parts over a high-street parts chain's own range, though another thought a Bosch-branded part from the chain should be fine.
• On a supercharged car, an owner recommends fitting a new O2 sensor anyway when running an OBD tuner. His had no fault codes, but the car felt better and the fuel trims were lower afterwards (about £70).
• For the post-cat sensor, see Replacing the post-cat lambda sensor.

NA: the MAP sensor and rough running

• An owner in 2006 says all NAs have a MAP sensor, which measures air pressure at the intake manifold (another owner corrected an earlier claim that it measures exhaust pressure). A faulty one can cause high fuel consumption and jerky throttle response. One owner replaced a faulty MAP and got an O2 sensor code rather than a MAP code, so a faulty sensor does not always set its own code.
• For a rough idle with vibration, other suggestions were a fuel or DIS (coil) pack problem, the throttle body potentiometers and connector, the crank sensor, the primary O2 sensor and a faulty fuel cut-off switch (one owner had the fuel pump running intermittently because of it, which made the car run badly).
• A dealer can run a full sensor and fuel pressure check, which one owner says is sometimes the quickest and cheapest route.
• See also EGR valve replacement for a related cause owners raised, and Throttle failure and the connectors.